Silver Meritorious Patron
First off, I don't know if there really are past lives. I just like the idea, so I entertain the idea. And I credit memories of them because it makes me happy and gives my life meaning. Sort of like a Christian believing that Jesus will take them up to Heaven where they will live in eternal bliss. Might not be true, but, hey, sure makes life easier to bear.
Or you could say that it's a sort of risk management. If you believe in God and that belief turns out to be right, you win. If you don't believe in God and you turn out to be wrong, oops, you lose. (If you don't believe and there is no God, then no win/loss. If you do believe and there is no God, then oops again.)