Shitty life? Did you realise you could have been reincarnated as the Dalai Lama? Then you would know what a shitty life really is.
Just like god, satanism and all the other cults in the world, if ya beleive in karma great if it dont exist in your world then fuck it its not an issue. Do you think the fucks in the middle east are feeling any karma at the moment. No matter how you term it its all the same, fate, dest.....met to be, karma...ect...its all bullshit.
I would think there is a karma or there isn't, and that Karma was a social institution of eastern religions to allow the poor to accept the opulence the priest classes lived in. But it's hard to disprove, so believe whatever you'd like.
The process is rather simplistic. My understanding of it doesn't effect my belief of social hierarchy explained in the dark ages. The system of Karma has been used to justify the Indian chaste system, which may be the most enduring form of slavery on the planet. Karma was also used in Buddhism to cement theocracies. You just couldn't explain your beliefs well. Your problem, not mine.
Perhaps this is your first life and your trials and tribulations will result in a life of magnificence the next time around so long as you maintain a good life throughout the duration of your misery.
If you believe it, it exists for you. If you believe in it, it has influence over you. The power of suggestion is much stronger than anyone would like to think. JMHO.
Quit focusing on the fact that you have a "shitty life" and do something about it. I have learned the hard way that sitting around whining about something doesn't initiate change...only action does. . Me, I got tired of being overweight...I wasn't exactly "fat", but I knew I could look better...so I took initiative, and it has worked: I have lost 15 lbs in the last 6 weeks, and I have been doing it the healthy way. I got sick of being depressed, so I broke out and did something about it. Trust me, it works.
karma aka "what goes around comes around"... doesnt everyone believe in that? Maybe you did something shitty in this life? I have also had a great vast stretch of a shit path to nowhere. I'm not blaming myself though. I blame my parents.
Who says you had to have done anything? Maybe you just have a tough lesson to learn this time around? The tough lessons are often taught via a harder than normal life.... which makes sense. You aren't going to learn nearly as much if the road is smooth, right? But what makes your life so much harder than others? How can you make a judgement without truely experiancing someone elses life? What looks easy from the outside might not be so easy from the inside. Is your life harder than those people "living" in Darfur? Its really a matter of perspective, is it not?