Many people believe in karma. There's nothing wrong with this, at some stage in their life many people have believed in the tooth fairy as well. Karma is actually one of the most brilliant of human creations. It is one of our most versatile psychological tools. It can make us feel better about our wretched and misery ridden lives. When everything has gone to hell it can be some comfort to think that better times are just around the corner even if you have to die first. This has the added advantage of giving people a reason to look forward to death which, let's face it, has got to be at least as helpful as the traditional whining and moaning with which it is usually greeted. Since death is going to happen anyway a somewhat relaxed attitude towards it is probably beneficial.
But the benefits of karma don't stop there. Possibly the most important thing karma does is give us a method of coming to terms with the success and good fortune of people we detest. This is vital because without it much of the population would explode with suppressed rage. For every shining moment such hated people have the remainder can console themselves with the knowledge that something truly horrible must be coming. Conversely those people themselves can look at their success and by extrapolating karma in the other direction convince themselves that they actually deserve it. Everybody's happy, or at least not killing each other in the streets, or at least not killing each other in the streets in greater than the usual quantities.
As theories go karma is great, everybody feels a bit better about themselves and assures themselves that judgement upon the unworthy will one day be dispensed by an even handed and all seeing universe (or God if you like). Of course there is the small matter of the fact that it is total bullshit but strangely that doesn't really matter very much. What karma or (insert similar religious/philosophic belief to your taste here) does for us doesn't actually depend on whether its true. It just depends on us believing it. In fact it doesn't even depend on that, it just depends on us pretending to believe it. We're not really deceiving ourselves, we're entering into a conspiracy with ourselves to promote a falsehood because we like it.
There is one of those desk calendar quotes which goes something along the lines of "If its stupid but it works then it isn't stupid". I would add a corollary to that, "If its wrong but it works then it isn't wrong". I realise that this will dissatisfy some, largely scientists (who want answers) and philosophers (who want questions) but for the bulk of humanity wrong but effective is more than good enough. Philosophers and scientists can make themselves happy by discovering the truth and everybody else will remain happy by ignoring them. This has worked well for us for millennia and continues to do so today. It can be claimed that the efforts of scientists and philosophers have added immeasurably to the well being of the human race and I would completely agree. However most of the human race would be equally happy with these achievements if you told them they were produced by sacrificing animals and dancing around an altar. I don't know how a television works and I don't care but if you told me that the programming quality could be improved by smearing fresh rabbit blood over the screen I'd be down at the pet store tomorrow.
Scientists claim it is important to know why things work and I would agree. However it is vastly more important that things work whether we know why or not. Knowing why something doesn't work is utterly useless unless in knowing that we are guiding to what will. If the option is between somebody saying "It is a scientific fact that we are all going to die" which is true and somebody else saying "believe in God and you can live forever" which is rubbish what one do you think is the more helpful? Neither will stop us dying but only one can make us feel a little happier while we do so.
Of course I'm one of those people who doesn't understand science and doesn't believe in karma. So what is left for me? Fortunately I've never really expected the universe to be fair.