I recall a math teacher, back in high school, who put us in our place a couple times when we thought we understood everything we needed to know and stopped asking questions, you know, typical teenage know-it-all... anyway, he'd say something like:

"young man, unless you change your attitude about learning, I probably have already forgotten more in my life than you will ever know in yours"

As others mentioned, I think the people who are at the peak of their profession, or hobby, are always looking to improve, to learn from someone else, and to be humble enough to know that they don't know it all... The ones who don't have that humility, can be a little scary with their obsession, and their belief that they already "know-it-all". It seems like the most respected folks in this forum are always willing to share what they know when they have some expertise, but, also seem genuine when they are asking a question, and enjoy learning about a technique, product, or tidbit of knowledge from someone else here. It's refreshing.