I like a good analogy so here's one for Karma that I made earlier. Karma is like a penny drop machine in an arcade. You put a penny in, and, fingers crossed, that penny will push more out, therefore rewarding you for the faith you had in the first place. Sometimes it happens straight away, with your first penny. Other times, it can take a while. You could spend a whole pound (doesn't sound like much but thats a hundred goes!) and get nothing in return. The key is to believe in it. If you have it in you to persevere, eventually you'll get that money to drop.
Karma. Keep doing good things, don't lose faith, and it will come back around. I think George Harrison can sum it up here:
It's gonna take time, a whole lot of precious time