If you consider yourself a mystic or a spiritual person, then I think it's safe to assume that you believe in reincarnation. Some sects of Christianity do not believe in this possibility, and I respect their beliefs. I am not trying to convince anyone that reincarnation is fact not fallacy. In fact, I am not trying convince anyone of anything, I am only sharing my views and beliefs with you.
This is a topic that greatly interests me; it certainly explains so many things that other theories fall short on.
For example, why do bad things happen to good people?
If you believe in reincarnation, then the answer is very simple. Sometimes, bad things happen to good people because they are paying off Karma from their past lives and learning things in the process (remember that journey towards enlightenment).
And while we are at it, let's make one thing clear: We all have Karma. If we managed to get a clean slate, that means we have reached enlightenment or self-realization which by definition wipes the slate clean. Only realized masters are free of Karma.
So what is Karma?
Karma is what you have accumulated in your past lives. Every time you do something you create Karma. One way to pay off your Karma faster is to do a lot of good deeds. Remember my Guru's declaration that Work is Worship. If you do service to mankind, animals, nature, etc., all of that counts as good Karma and it takes away from the negatives you've accumulated over the ages and different lifetimes.
When we incarnate to a new life in a new body, our purpose is to learn lessons and pay off Karma. When we've paid off Karma and we incarnate as an enlightened master, then we are helping other people pay off their Karma.
I wish you all a speedy payment of your Karma. May your slate be clean in a jiffy!