Karma.

People say, Karma is a b*tch. But thinking back at whatever you or anyone has done, did "she" actually condemn you out of the wrong reason? Everything you do for others will eventually get back at you, be it the good deeds or the bad things you did.
And Karma works both ways, because of somebody did something kind or hurtful to you, they will get it back.
Because, what goes around comes around.