Karma is based on logic. It is an unavoidable consequence of our creations. When we create anything, we also create other things which might not be what we intended.
EXAMPLe:
If you do something good, enjoy your life. If you do something bad, you'll get something bad.
A good phrase to describe Karma is, "Every Action has an equal or opposing reaction".
what goes around comes around, it could be good or it could be bad....