The #1 mistake is not talking to your users. The most important thing to do at a startup is set up a fast feedback cycle and get on the path of constant improvement. There’s almost no way the first thing you do is awesome, so don’t expect that. Instead, expect to be constantly improving your product, and your north star is your user/customer. As a rule, your only shot at building a successful startup is if you build something that people truly love. Too many startups operate in the corner without any north star or feedback loop, and end up wasting a lot of time.
The #2 mistake is not hustling enough. You should not expect building a company to be easy. If you expect to be successful, your company has to be your #1 priority at basically all times, above friends, fun, sleep, significant others, etc. If something comes up, it is your responsibility to get it done. For example, in the early days of Scale, if a task wasn’t being completed quickly enough, I set up a Twilio alert that would call me to wake me up if I were asleep. I didn’t get much continuous sleep. Without that, it’s unclear if we would’ve ever gotten off the ground.
Some other serious mistakes that I see often:
Hiring bad people. You should only hire people who are insanely great. Otherwise, you will regret it with probability 1.
Hiring people too early. Don’t hire people before you have a really clear idea of what you want them to do.
Hiring people too late. Hire people right when you have enough extra work for 1 more person. Much later than that and you’ll hamstring your growth.
Lying to yourself. There’s a fine line between having conviction and ignoring data. Don’t ignore data.
Not being prepared for hardship. There will be ups and downs.
Getting caught up in startup pageantry. Especially these days, there are a lot of startup events, founder dinners, parties, conferences, etc. Those are usually wastes of time.
Not shipping enough. Your velocity will only get slower as you grow. If you are not shipping insanely quickly initially (multiple new features every day), there’s very little chance you’ll succeed. You also need to be good at coding to do this. Be good at coding.
Focusing on competitors. If you want to get stuck in a crappy zero sum game, focus on your competitors. Otherwise, focus on building something intrinsically awesome.
Not protecting an early culture of getting shit done. The early stages of a startup are incredibly fragile. You need to do whatever you can to maintain a strain of raw startup energy as you grow the company. That means you need to live it yourself, fire detractors, and reward promoters.
Being too focused on fundraising. It’s a very common mistake. Money matters, but few problems in an early stage start are solved with money. You can’t build a great product by spending money on it. You want employees who would rather be paid in equity than cash. Your valuations along the way don’t really matter. It’s what you exit at that matters. Focus on getting great people instead.