It is important to know that we live in cold world. By that, we mean being good does not always result in getting rewarded unlike what fairy tales or movies display. In the real world, bad individuals are often rewarded for their bad acts while the good are punished. Knowing this and still continuing to do good takes true willpower.
When you do a heroic act that involves self sacrifice, the person saved may feel grateful for a bit, and may also be selfishly glad that you sacrificed yourself to save them. Some people may feel entitled to be saved, and may not actually be grateful at all. This is the world we live in, where many people are scumbags.