What have I learned from YC's users, the startups we've funded?

...most startups have the same problems.

...the batch that broke YC was a powerful demonstration of how individualized the process of advising startups has to be.

...founders can be [bad] at realizing what their problems are. Founders will sometimes come in to talk about some problem, and we'll discover another much bigger one in the course of the conversation.

Often founders know what their problems are, but not their relative importance.

Focus is doubly important for early stage startups, because not only do they have a hundred different problems, they don't have anyone to work on them except the founders. If the founders focus on things that don't matter, there's no one focusing on the things that do.

Speed defines startups. Focus enables speed. YC improves focus.

Why are founders uncertain about what to do? Partly because startups almost by definition are doing something new, which means no one knows how to do it yet, or in most cases even what "it" is.