It is the simple science of cause and effect. In biblical terms “we reap what we sow.” According to the Law of Karma, the good actions or karmas will cause positive or desirable experiences while the negative or “bad” actions or karmas will cause undesirable experiences. 
It is very popular to say “well karma is going to catch up with you…or “karma’s a bitch.” What is not recognized is that much of our karmic debt was set before this life time.
Swami Satyananada has said that “man cannot change his karma.” “All karma whether it is perceived to be good or bad must be lived through. There is no way around it. Karmas are unalterable. Karmas are like seeds. When they fall from the tree, they sprout.” 
We may be working through karmas of many life times not just from the one we are currently living. Knowing this may not make it any easier to deal with present life situations. However, if we understand that that our karma was put in place before we showed up in this lifetime perhaps we can work to exhaust it through a more positive attitude of grace and acceptance.
So this year I resolve to accept that every experience, perceived desirable or undesirable, is inevitable karma and part of my current life journey.
Through being the witness, of my thoughts, words, and actions I endeavor not to take on any new undesirable karma in 2013.
The future me will be thankful.Resources 1. SYA Academy (2006) Cleveland, Ohio, USA 2. SYA Academy (2006) Cleveland, Ohio, USA 3. Saraswati, Sw. Satyananda (2006), Karma, Yoga Magazine, August.