Evil is done by oneself alone;
By oneself is one defiled.
Evil is avoided by oneself;
By oneself alone is one purified.
Purity and impurity depend on oneself;
No one can purify another.
Dhammapada v. 165, translated by Gil Fronsdal
To my mind, this verse is a powerful corollary to the whole idea of karma, or “we reap what we sow”. Our inclination to blame our bad actions on outside forces is deeply ingrained, but it points in exactly the wrong direction. Even if we are sorely provoked, we have to own our behavior. Even if it looks as if there was no other option than bopping someone on the head, there actually was at least one other option.
And if we do something kind, deflecting painful energy, or spontaneously generating happiness or peace, we are purified.
When we’re feeling bad, we often look to outside circumstances for causes of our bad feelings, and some causes are external. This is why we make the effort to put ourselves in wholesome situations, with people we respect. But even in the best set of circumstances (in a loving family, or a monastic setting), negative feelings come up. Rather than letting our feelings drive us to (attempt to) rearrange the outside world, we need to first look inside – what is the real source of our dissatisfaction? Is it that the world doesn’t accommodate our desires?
We can rearrange our internal furniture to minimize suffering and promote wholesome attitudes and behaviors; we can adjust our expectations of others and of ourselves. When we (inevitably) meet with dukkha (unsatisfactoriness), we can stamp our foot and demand something better, or we can look inside to try to discover the source of our unhappiness and apply patient endurance as an effective purification exercise.