Anyone can buy a motorcycle and ride it, that is not really impressive, but I think it takes a special kind of person to be able to take a kit of random parts and transform it into a smooth running machine that will take them where they want to go and back with no trouble.
I'm not talking about those who slap a kit onto a Craigslist bike and then resell it, I am talking about those who can port and polish and fabricate their own parts, tweak and tune for maximum performance, etc.
For some, it is the attention they get from riding a motorized bicycle, seeing everyone's head swivel around and follow you as you go by.
For others, it is the satisfaction of building something with your own hands, and showing off your work.