Selfishness causes some people to kill their unborn children. The child isn't convenient for them at the moment, and it wasn't convenient for them to take precautions beforehand. Most people vote based on selfishness. Selfishness causes some people to take more from society than they give in return. Selfishness causes some people to complain about the lack of police protection and high taxes simultaneously.
Selfishness causes others to simultaneously complain about poor public education and high taxes.
Obviously, there are exceptions here. Some schools do a poor job of educatiing children even with large budgets. War is caused by selfishness on the part of at least one country. Divorce is a product of the selfish desires of at least one of the two people involved. The goal of each member in a marriage should be to unselfishly give more than they take.