The 10 Biggest Startup Mistakes

The Most Common Founder Mistakes and How to Avoid Them …

Starting a technology company is relatively easy these days. Building one that survives, finds product-market fit, creates repeatable demand and becomes a sustainable business is considerably harder. There is no shortage of advice for founders, such as books, podcasts, accelerators, investors, consultants, frameworks, blog sites like this one and an endless stream of people telling entrepreneurs how they should build their businesses. Yet startups continue to make many of the same mistakes. Research from CB Insights provides a useful reality check. Its latest analysis of 431 VC-backed companies that shut down since 2023 found that 70% had run out of capital. However, CB Insights makes an important distinction: running out of money is usually the final cause of death rather than the root cause. Poor product-market fit was cited in 43% of failures, bad timing or macro conditions in 29%, and unsustainable unit economics in 19%. Here are the ten mistakes I believe founders should take most seriously.

Top 10 Startup Mistakes

1. Building Something the Market Does Not Need

Failure research: 43% cited poor product-market fit.

This is the biggest mistake because everything else becomes irrelevant if customers do not care enough about your product to buy it. Founders can become emotionally attached to their technology. They see the problem clearly, understand the elegance of their solution and convince themselves that the market will eventually catch up. What founders fail to understand is that “we can build it” is not the same as “people will buy it.” CB Insights’ latest research found poor product-market fit in 43% of failed VC-backed companies. Two-thirds of the companies where PMF was cited as a failure reason were early-stage businesses that never found a genuine market.

Why founders make the mistake: They fall in love with the solution rather than the problem.

How to avoid it: Sell before you build too much. Talk to prospects. Test willingness to pay. Challenge your assumptions. Let customers shape the product rather than simply validating what the founder already wants to believe.

2. Running Out of Money Before Proving the Business

Failure research: 70% of recent failures ran out of capital.

This is the most frequently reported failure event in the latest CB Insights research, but it’s important not to misunderstand the statistic. Running out of money is often the consequence of something that happened earlier, such as weak demand, poor economics, excessive spending, slow sales or an inability to raise additional funding.

The 431 failed companies analysed by CB Insights had collectively raised $17.5 billion, demonstrating that funding alone does not rescue a fundamentally broken business.

Why founders make the mistake: Optimism. Founders routinely believe the next product release, major customer, funding round or market opportunity will arrive before the cash runs out.

How to avoid it: Manage the runway aggressively. Build scenarios around revenue, pipeline, hiring, product development and fundraising. Know exactly what milestones must be achieved before the next funding requirement appears.

3. Treating Marketing as an Expense Rather Than a Growth Engine

Failure research: Poor marketing was cited in 14% of failures.

This is particularly relevant to technology startups. Some founders will spend hundreds of thousands developing a product but regard £50,000 of marketing as an extravagance. That makes little commercial sense, as a great product that nobody knows about is not a business. Marketing creates awareness, positioning, demand, credibility, market education and the flow of potential customers into the sales process. It also gives salespeople the tools and narrative they need to have productive conversations. Research from BCG has found that companies that successfully integrate marketing and sales can achieve 15–30% improvements in marketing efficiency, 20–50% increases in digital ROI and two-to threefold improvements in marketing-driven lead conversion.

Why founders make the mistake: Product and engineering feel tangible. Marketing can feel subjective, particularly when the founder doesn’t understand it and has never managed a marketing function.

How to avoid it: Build marketing into the business plan from the beginning. Do not simply budget for a website, some LinkedIn posts and a few events. Work backwards from the revenue target and calculate the demand, pipeline and market coverage required.

4. Failing to Put Proper Marketing Leadership in Place

This is closely related to underinvestment, but it deserves separate attention. A startup does not necessarily need a CMO on day one, but there comes a point where marketing becomes too strategically important to be managed as a collection of disconnected activities.

Someone needs to own:

• Positioning
• Messaging
• ICP definition
• Market segmentation
• Brand
• Demand generation
• Content
• Marketing technology
• Data
• Pipeline contribution
• Marketing performance
• Alignment with sales

That person does not necessarily need the CMO title. They do, however, need sufficient seniority to influence the company.

Why founders make the mistake: They mistakenly assume marketing is something a junior marketer, agency or salesperson can “do.”

How to avoid it: Hire marketing leadership when the complexity of the growth challenge exceeds the founder’s ability to manage it effectively. The objective is not to acquire a fancy title; it’s to put someone accountable for creating and maintaining a repeatable marketing engine.

5. Putting Marketing Under Sales

Marketing and sales must be fully aligned and work together, but they should not be confused with each other. One of the most damaging organisational mistakes is allowing sales to dictate marketing because sales is closer to revenue. This often turns marketing into a sales-support function: make some presentations, create a brochure, organise an event, generate some leads and respond to whatever random requirements the sales team asks for this week. That’s not strategic marketing. BCG’s research shows that organisations integrating marketing and sales can materially improve efficiency, digital ROI and conversion. Marketing needs to contribute to revenue, but it also needs responsibility for market understanding, positioning, demand creation and long-term brand value.

Why founders make the mistake: The sales team’s output produces immediate, visible activity. Marketing’s contribution is usually less direct and immediate.

How to avoid it: Make marketing and sales equal peers with shared commercial objectives. Sales must provide market feedback. Marketing must create demand and equip sales. Neither function must be allowed to own the other.

6. Founders Refusing to Let Functional Leaders Do Their Jobs

Founder involvement is essential. However, constant founder interference at a granular level is not. There is a point in every startup when the founder must stop being the chief product manager, chief salesperson, chief marketer, chief recruiter and chief customer-service manager. If you have hired an experienced marketing leader but continue rewriting every piece of messaging, changing campaign priorities and overriding positioning decisions, you have not actually hired a marketing leader; you have hired an executor. The same applies to sales, product, finance, technology and operations.

Why founders make the mistake: The company is their creation, so they have an invisible umbilical cord connecting them and a close emotional attachment. They know the history, understand the original vision and often believe nobody can represent it as well as they can.

How to avoid it: Define who has the authority to make decisions. Founders must own purpose, vision, strategy and major decisions. Functional leaders must own their functions. The founder’s job changes as the company grows and experienced professionals are onboarded to run business functions. The objective is not to know more about every function than the people running them; it’s to ensure those people are aligned with all other functions so everyone is working towards the same company objective.

7. Changing the Message Every Five Minutes

Founders are particularly vulnerable to messaging interference. A marketing team spends weeks defining the ICP, positioning, messaging architecture, website and campaign strategy. Then the founder attends a conference, meets an interesting prospect, someone tells them about a new market and suddenly the messaging changes, again. Then the website needs rewriting, campaigns need changing, the product needs repositioning and everyone is in a panic thanks to this strategic whiplash.

Why founders make the mistake: Founders are naturally curious and opportunistic. They also tend to believe every interesting conversation represents a new opportunity.

How to avoid it: Agree on the positioning and messaging as part of the strategy. Change it only when the evidence changes, not because someone had an interesting conversation at a networking event.

Remember:

• Consistency creates recognition
• Recognition creates credibility
• Credibility creates demand

8. Chasing Shiny New Toys Instead of Following the Plan

CB Insights’ research identified lost focus in 13% of startup failures, and that statistic should worry every founder. Startups have limited money, people and time, yet founders regularly introduce new ideas faster than the organisation can absorb or execute them.

Typical founder distractions include a new:

• Market
• Product
• Geographic territory
• Technology
• AI opportunity
• A partnership.
• Enterprise customer asking for bespoke functionality

Individually, these ideas may be good, but collectively they can destroy a startup’s focus and lead them down the path of self-destruction.

Why founders make the mistake: Entrepreneurs are opportunity machines. The same curiosity that helped create the company can become a liability when there is no discipline around what the company will not do.

How to avoid it: Maintain a clear plan and force every new idea to answer three questions:

1. Does it support our strategy?
2. Can we fund it?
3. Can we execute it without damaging what we are already doing?

If the answer is no to any of the three questions, put the idea on the shelf and get back to work.

9. Ignoring The Importance of Founder-Led Sales

Most tech entrepreneurs tend to fully develop their products before getting feedback from potential buyers. This is one of the strangest startup behaviours. A founder creates a company because they believe they have identified an important problem. Then they disappear into product development. Six months later, they emerge with a product and discover that selling it is considerably harder than building it. Research published by Harvard Business Review found that salesmanship is central to startup success, yet many entrepreneurs delay selling. More than half of the 120 entrepreneurs studied across six countries fully developed their products before getting feedback from potential buyers. More recent HBR research, based on interviews with more than 250 founders, argues that today’s environment makes founder-led sales even more challenging — and more important — because buyers are increasingly crowded with competing propositions and more sceptical of unfamiliar vendors.

Why founders make the mistake: Selling feels uncomfortable, while building products feels productive. Founders often believe that once the product is good enough, customers will naturally appear.

How to avoid it: Founders must start selling early and be personally involved in the sales process at the beginning. The founder needs to understand the buyer’s language, objections, economics, buying process and willingness to pay. That intelligence is invaluable before attempting to build a repeatable sales machine.

10. Forgetting That Focused Execution Beats Endless Ideas

The final mistake is really the combination of several of the others: Failing to execute consistently. Startups do not need 25 strategic initiatives. They need a small number of things done extremely well. A company with one clear ICP, one compelling proposition, one focused market and a disciplined go-to-market strategy will often outperform a company with a dozen opportunities and insufficient resources to pursue any of them properly. Research from CB Insights found that startups lost focus in 13% of failure post-mortems. It also found that 13% cited product timing and 10% cited a failed pivot. The lesson is not to “never change strategy,” but only to change it deliberately when the evidence supports the decision.

Why founders make the mistake: Founders can mistake activity for progress.

How to avoid it: Establish a handful of measurable company objectives and make every department accountable for contributing to them. New ideas must compete for resources rather than automatically receiving them.

What Can We Learn?

There is a temptation to look at startup failure statistics and conclude that money is the biggest problem, when that is not necessarily the case. Money is frequently where the story ends, but the deeper problem is failing to create a business that can generate sustainable demand and economics before the money runs out. This is where marketing becomes critically important. Marketing is not the answer to poor product-market fit, because you cannot rescue a product nobody wants. It cannot compensate for fundamentally broken economics, but once there is a genuine market opportunity, underinvestment in marketing can be equally dangerous.

The evidence increasingly points towards a simple commercial reality: Startups need to invest in the ability to understand their market, position their proposition, create demand, generate qualified opportunities and build a repeatable route to revenue. A 2026 study from HEC Paris involving more than 300 B2B high-tech startups is particularly interesting. It found that investing in the development of salespeople delivers the strongest revenue effect in the early stages: A 10-point increase in budget allocation to personal selling was associated with almost a 50% increase in revenue. Once product-market fit had been achieved, mass-media marketing became more effective, with the same budget shift expanding the customer base by around 12%. That suggests startups must invest in the right go-to-market capability at the right stage. Early on, that means founders talking to customers and selling. Then, as the business finds product-market fit, it means building marketing capability that can create awareness, demand and scalable customer acquisition.

Marketing First

Eventually it means building a professional marketing organisation capable of operating alongside sales rather than underneath it, because ultimately, selling to other businesses is the hardest thing a startup must do. You can hire developers to build the product, buy technology, raise money, rent an office, build a website, but getting another company to part with its money and trust you with a business problem is a very different proposition. That is why founders need to sell and why marketing needs to be taken seriously. By that I mean founders must invest appropriately in marketing, ensuring it is supported and given time to develop. That is why the startups most likely to succeed are not necessarily the ones with the most brilliant technology. They are the ones who combine a real market need with disciplined execution, strong leadership, focused sales and sufficient investment in marketing to make the market understand why they should buy. The biggest startup mistake is not making one bad decision. The evidence shows it’s repeatedly making small, avoidable mistakes until there is no money left to fix them.

You may want to read: “Why Startups Must Take Target Data Seriously.”