In the Buddha’s teaching, there’s no question of a person’s “deserving” happiness or “deserving” pain. The principle of kamma is an impersonal one: that there are actions leading to pleasure and actions leading to pain.

 "A proper understanding of kamma helps to correct the false idea that if people are suffering they deserve to suffer, so you might as well be equanimous and just leave them alone. When you catch yourself thinking in those terms, try to keep four principles in mind.

First, remember that when you look at people, you can’t see all the karmic seeds from their past actions. They may be experiencing the results of past bad actions, but you don’t know when those seeds will stop sprouting. Also, you have no idea what other seeds, what wonderful latent potentials, will sprout in their place.

There’s a saying in some Buddhist circles that if you want to see a person’s past actions, you look at his present condition; if you want to see his future condition, you look at his present actions. This principle, however, is based on a basic misperception: that we each have a single karmic account, and what we see in the present is the current running balance in each person’s account. Actually, no one’s karmic history is a single account. It’s composed of the many different seeds planted in many places through the many different actions we’ve done in the past, each seed maturing at its own rate. Some of these seeds have already sprouted and disappeared; some are sprouting now; some will sprout in the future. This means that a person’s present condition reflects only a small portion of his or her past actions. As for the other seeds, you can’t see them at all.

This reflection helps you when developing compassion, for it reminds you that you never know when the possibility to help somebody can have an effect. The seeds of the other person’s past bad actions may be flowering right now but they could die at any time. You may happen to be the person who’s there to help when that person is ready to receive help.

The same pattern applies to empathetic joy. Suppose that your neighbor is wealthier than you are. You may resist feeling empathetic joy for him because you think, “He’s already well-off, while I’m still struggling. Why should I wish him to be even happier than he is?” If you find yourself thinking in those terms, remind yourself that you don’t know what your karmic seeds are; you don’t know what his karmic seeds are. Maybe his good karmic seeds are about to die. Do you want them to die any faster? Does his happiness diminish yours? What kind of attitude is that?

The second principle to keep in mind is that, in the Buddha’s teaching, there’s no question of a person’s “deserving” happiness or “deserving” pain. The principle of kamma is an impersonal one: that there are actions leading to pleasure and actions leading to pain. In this way, it’s not a respecter of persons; it’s purely an issue of actions and results. Good people may have some bad actions squirreled away in their past. People who seem horrible now may have some wonderful actions in theirs. You never know. The Buddha didn’t create the principle of kamma, or say that it’s good or just. He simply pointed out the way actions produce results.

So there’s no question of a person’s deserving or not deserving pleasure or pain. There’s simply the principle that actions have results and that your present experience of pleasure or pain is the combined result of past and present actions. You may have some very unskillful actions in your past, but if you learn to think and act skillfully when those actions bear fruit in the present, you don’t have to suffer.

A third principle applies to the question of whether the person who’s suffering “deserves” your compassion. Because no human being has a totally pure karmic past, if you make a person’s purity the basis for extending your compassion, there will be no one to whom you can extend it.

Some people resist the idea that, for example, children born into a warzone, suffering from brutality and starvation, are there for a karmic reason. It seems heartless, they say, to attribute these sufferings to kamma from past lives. The only heartlessness here, though, is the insistence that people are worthy of compassion only if they are innocent of any wrongdoing. Actually, people who are doing wrong are just as deserving of our compassion as those who are being wronged. There’s no need to like or admire the people for whom you feel compassion. All you have to do is wish for them to be happy. Then you do what you can to alleviate the suffering that comes from past mistakes and to stop the mistaken behavior that causes suffering now and into the future. The more you can develop this attitude toward people you know have misbehaved or are misbehaving, the more you’ll be able to trust your intentions in any situation.

The fourth principle to remember concerns the kamma you’re creating right now in reaction to other people’s pleasure and pain. If you’re resentful of somebody else’s happiness, someday when you get happy there’s going to be somebody resentful of yours. So ask yourself: Would you want that? Or if you’re hard-hearted toward somebody who’s suffering right now, someday you may face the same sort of suffering. Would you want people to be hard-hearted toward you? Always remember that your reactions are a form of kamma, so be mindful to create the kind of kamma that gives the results you’d like to see."

~ Thanissaro Bhikkhu "The Sublime Attitudes: A Study Guide on the Brahmavihāras"