Now that title might seem a bit shocking, but think about this for a moment: An egoistic person will never really feel happy, so if you strive for your own happiness, that is an impossible goal, but you can make someone happy even if for a moment. So we are the source of our one another's happiness, but not of our own.
Just because someone deserved their suffering, doesn't mean, if the person is suffering, we can't help them. We can reduce their suffering a little, and that gives us good Karma.
People suffer out of vanity and ignorance to the laws of Karma. They suffer because they deserve to suffer. SOURCE: If karma is real, doesn't that mean everyone that is suffering deserves it? @ Reddit
Thirst is the path to suffering. The Buddhist tradition identifies taṇhā as a self-centered type of desire that is based in ignorance. This type of desire is contrasted to wholesome types of desire such as the desire to benefit others or to follow the Buddhist path. SOURCE: Tanha (thirst/desire) @ Wiki