We've definitely missed good startups. But one advantage of having so many competitors is that we're much more likely now to learn when we screw up. When a startup from one of the other YC-like organizations does well, I often check their YC application to see how we missed them. Usually it's because they were good guys but working on a terrible idea, which they later changed. So in response to that we now make a conscious effort to pay less attention to the idea and more to the people when we read applications.
We wouldn't fund a group if the founders were really lacking, e.g. if they seemed uncommitted, or not smart enough to build whatever they were planning to.
we now make a conscious effort to pay less
attention to the idea and more to the people
...
We wouldn't fund [people who were] not smart
enough to build whatever they were planning to
These comments don't seem entirely non-contradictory. Wouldn't you ever say "I don't think you're smart enough to make that work, but how about working on a less ambitious problem"?