There is nothing that is a more certain sign of insanity than to do the same thing over and over and expect the results to be different. Albert Einstein

Curiosity is the best guide. Your curiosity never lies; it knows more than you do about what's worth paying attention to.

When you have an idea for a startup, ask yourself. who wants this right now? Who wants this so much that they'll use it even when it's a crappy version one made by a two-person startup they've never heard of? If you can't answer that, the idea is probably bad.