And also memory is very tricky. I imagine there are lots of people who met Zuckerberg thought he didn't have it took, but now believe they always thought we was going to succeed. That's why I suggest angel investors write down everything they thought about an encounter with someone immediately after the meeting. Why you think they'd succeed and fail? Then when you follow them in the future you can compare your notes to what happened and learn. Otherwise it's really easy for your brain to put together a completely unrealistic view of what happened in the past based on what's happened since.
I remember an article where someone said they were doing this in the Army, writing / saying "this guy has the potential to be great" or "this guy will wash out quickly", and discovering 20 years later that their predictions had no relationship to reality. (Can't find that article anymore though.)
In Facebook's amazing case, Zuck got $500K from Thiel almost immediately out of the gate, after a little traction and a bunch of backstabbing as to who at Harvard college controlled the company.
