Pleasure and pain are effects. The fact that they change shows that they depend on causes. This is why you will not experience the pleasure you want unless you create its causes; and you will prevent the suffering you want to avoid by giving up its causes. As soon as a cause of pain is inscribed in your mental continuum, you will have to go through its effects whether or not you would prefer to avoid suffering.
The effect of harmful actions is based on the intensity of the delusions that motivate them. Our present happiness or our present unhappiness are nothing other than the result of past actions.
The Dalai Lama