This is a wise essay from Paul Graham on why many start-ups fail while others succeed. The difference is that the founders who build a start-up to solve their own problems versus what they think people need:
Why do so many founders build things no one wants? Because they begin by trying to think of startup ideas. That m.o. is doubly dangerous: it doesn’t merely yield few good ideas; it yields bad ideas that sound plausible enough to fool you into working on them.
At YC we call these “made-up” or “sitcom” startup ideas. Imagine one of the characters on a TV show was starting a startup. The writers would have to invent something for it to do. But coming up with good startup ideas is hard. It’s not something you can do for the asking. So (unless they got amazingly lucky) the writers would come up with an idea that sounded plausible, but was actually bad.
For example, a social network for pet owners. It doesn’t sound obviously mistaken. Millions of people have pets. Often they care a lot about their pets and spend a lot of money on them. Surely many of these people would like a site where they could talk to other pet owners. Not all of them perhaps, but if just 2 or 3 percent were regular visitors, you could have millions of users. You could serve them targeted offers, and maybe charge for premium features.
The danger of an idea like this is that when you run it by your friends with pets, they don’t say “I would never use this.” They say “Yeah, maybe I could see using something like that.” Even when the startup launches, it will sound plausible to a lot of people. They don’t want to use it themselves, at least not right now, but they could imagine other people wanting it. Sum that reaction across the entire population, and you have zero users.
You should read the whole post here.