The Sherpas play a very important role in most mountaineering expeditions, and in fact many of them lead along the ridges and up to the summit.
Good planning is important. I've also regarded a sense of humor as one of the most important things on a big expedition. When you're in a difficult or dangerous situation, or when you're depressed about the chances of success, someone who can make you laugh eases the tension.
I was extremely lucky that I had two great wives. It sounds a bit funny to say that, but it's absolutely true.
I think Himalayan climbers tend to mature fairly late. I think most of the successful Himalayan climbers have ranged from 28 to just over 40, really.