I believe in luck simply because if something fortuitous happens to me, it's not necessarily happened because I planned it that way, or because 'fate' decided it would happen. It is because it happened to happen in that happenstance. Therefore, it would be luck that made it happen. I will say that I don't think there is a good luck or bad luck, just that things happen that are not expected. Luck, whether good or bad, makes that occur.