My best answer right now is a quote from Pieter's MAKE book:

Solve your own problems

The most important thing is to find ideas from solving your own problems. You do that by looking at your own life and observing what your daily challenges are. Then you see if you could make those challenges easier using technology. If you solve your own problem, it's very realistic that there's many more people like you who would also love their problem solved. And that's pretty much what a business is. Solving lots of people's problems in return for money.

In startups, this business can be in the form of an application, a website or even only just a physical service tied together with some technology.

Link: makebook.io/#2-2