#1 Run out of cash.

The number one reason why startups fail is that they run out of cash. Founders need to be very strategic about what they spend their money on. If you spend money on a product, make sure this is a product that customers need. If you spend money on marketing, make sure that every $ you spend is well spent on acquiring customers.

Focus on having positive cash flow at all times i.e. more money goes into the company than out of it. Either track your expenses or hire an accountant or CFO to manage finances.

#2 Don't establish product market fit.

Founders spend months and years working on a product they think their customers need only to find out that there is no demand and market for their product. Savvy founders spend their time speaking to customers, iterating and gathering feedback to build a product that fills a demand in their target market. Most importantly it solves a clear problem that customers have.

Collect customer feedback, iterate and pivot when needed to build the right product. Don't assume what the customer needs.

#3 Founders conflict.

Starting a startup with a co-founder is like committing to a marriage. Co-founders have to stick with each other through thick and thin and spend years side by side with the aim of building something great. However, the author of the book "The Founder's Dilemmas" found that 65% of startups fail due to conflict among co-founders.

Pick a co-founder that ideally has similar values to you and deeply believes in the mission of the startup.