I agree with most above that humility is a personal issue, not necessarily related to the art.
I have found that many aikidoka are not necessarily sure of themselves or their aikido and sort of have a complex about it. Not sure why other than the fact that we don't have competitions and don't really measure against others. This is both good and bad. Good since you should be studying the art to measure against your internal self. Bad because without a measure and the martial maturity many end up questioning their aikido or martial effectiveness.
I think this lack of self confidence can sometimes be confused with humility. I think they are two distinct things.
I have constantly struggled with humility throughout the years I have been a martial artist. It comes and goes. Like last night when I was at the gym watching some TKD guys trying to do self defense stuff. I really wanted to get in there and show them how to do it right!! It was painful to watch!
However, having been KO'd at least once by an axe kick....I certainly was humbled that day!