This has been on my mind lately as well, for some reason. That, and the point of this story
http://sivers.org/horses which is basically that even after the fact, it's really hard to know anything[1].
I don't know if it's just from growing older but I feel a lot more humble when looking at peoples ideas and actions than earlier. I literally feel that I have no clue whether they will succeed or not whereas I used to quickly get quite strong feelings in one direction or the other. In one way, this feels more mature and zen but at the same time, it annoys me a bit. I feel that conviction is the trait of a leader and something I need to possess if I want to convince anybody to engage in my projects. Maybe I'll just practice faking it and hope they didn't read this comment :-)
Edit: [1] One of my favorite examples of this is in Felix Denis' book How To Get Rich where he describes that the problem with Apple is Steve Jobs. This was written 7 years ago when Apple was struggling and it looked like Steve Jobs was driving it into the ground with his stubbornness. (The book is excellent by the way, in spite of the tacky sounding title)