Lack of focus kills startups.
In the early stages of a new company, you need extreme focus because you barely have any resources or time. That's why one of my favorite sayings is, "Your focus needs more focus."
It’s a simple trick—focus—but it's incredibly hard to do given that you have a very powerful computer in your pocket and no shortage of things you could be doing with your time.
But if you focus, you're going to make progress towards whatever your goal is. If you don’t, then you’re going to dilly-dally. Your time will be taken up by fake work. You'll end up playing startup, instead of building and growing your startup.