What makes one startup more successful than another? A large part of the answer is team and timing. However, startups should also have a unique insight on the world. This insight is a psychological one or an engineering one. Psychological insights are things Facebook, which exploits voyeuristic nature of social interaction. (on a higher level, FB exploits mimetic desire, which is the theory of Rene Girard and the reason Peter Thiel was the first investor in FB.)
Of course, some desires are obvious. For example, people would love to be able to buy things cheaper and get them faster. How that happens is not obvious. In fact, it can be a massively capital and engineering talent intensive proposition (Amazon). For instance, a product like Google is obviously helpful. Realizing that consumers want relevant information (search) as fast as possible for free to the end user is not much of an insight. Figuring out how to do it, is quite the insight.
Some startups have a great psychology insight and a technically trivial solution. Other startups come up with a technology insight and a psychologically trivial solution. Of course, some startups mix and match both. What is your insight? Is it a new way to engineer an algorithm or uncovering an unserved human desire or both?
A few psychological insights: Tinder, Twitter, Uber and AirBnB.
A few engineering insights: Bitcoin, Heroku and Akami.