Lucky Duck

It's St. Patrick's day. Yep. I wonder why we really celebrate this day to be honest. The images that come to mind are pots of gold, little men, and of course luck.
I must admit, I'm a lucky person. What is luck really? How do you define luck? Why do some of us seem to have it, and others seem to have "bad luck" - is there even such a thing as bad luck?
Is good luck just positive thinking and the brain finding a way to make good things happen? Is bad luck the result of bad choices? If so, what about all of those people who seem to be constantly faced with "bad luck"?
Hhmmm...