I have a friend from school who got cancer. At one point, he needed blood transfusions to survive. I realized that in a few minutes of my time (less time than I spend every week standing around waiting for public transport) I could help someone.

Producing blood is easy, my body does it automatically. Donating is easy, all I have to do is sit there. Donating is much less painful than banging my shin on the coffee table or accidentally rubbing my eye after chopping up hot peppers.

I get to know that someone else will survive, or they won't lose a friend, parent, spouse, sibling, or child.