Why shouldn't you? Karma is unreliable in the sense that if you want to believe it, than it is true, but if choose not then it actually is not. Why? The conscience decision of accepting karma as true will cause you to see what you think you should see by using selective observations while ignoring others. You will take into account only observations of good decisions which lead to good consequences, and bad decisions which lead to bad consequences, while ignoring their inverses. Basically, Karma is the cause of itself; it causes itself in those who believe it, but not for those who don't because it has no effect on their conscience. Karma is an illusion which distorts one's perception on reality; a reality which Karma does exist.