There is a element of luck to it I think.
I know it's mostly luck.
I got two of them 10 days apart, 36 years ago. My only two--both six irons.
And I am known as a crummy iron player.
I also holed a six iron off my drive for deuce in a scramble once, and a 23* fairway wood from 210 for deuce on the same hole.
Then nothing for about 10 or so years until I holed a nine iron for 2 on the second at my current home course.
But, unlike Brad, I've seen at least three aces besides my two.
The best one was in a club league match where my teammate's opponent holed one, so my teammate stood up and said, "Looks like I have to hole it for a half."
Then he proceeded to hit the flagstick on the fly--failed to hold the green, however..