Self-interest and drives
A human is a being that wants to survive and reproduce (this tendency is from the self-replicative nature of the genes and cells), hence he works for his survival and reproduction. That gives rise to self-interest. He works for his survival and reproduction. The genes want him to live, and does not care about the others, hence his basic motivation is to make sure that he himself lives. This is the origin of self-interest.
The society is an abstract entity which is formed by a group of people depending on each other for mutual help in surviving and satisfaction of other desires, and hence it likes people to be not too selfish and care for others too.
However, it is interesting to note that societies in general tend to resist selfishness within the society, not between the society as a whole with another society. For example, consider a country, selfishness is resisted within a country, but one country's people may have societally acceptable hatred for people of other countries.
This concept can be easily seen in this example: Egotist tendencies are opposed by a society in general, i.e. if a person favors himself incessantly and strongly, then other people in general will not like it, and this is not viewed as correct by most societies. BUT if we extend our identity (i.e. ego) to a bigger group entity, for example, a country, then its okay if I cheer for my country and very strongly show favor for it against other countries. This behavior is acceptable to all societies, but this is nothing but egotitistic behavior, since we have extended our identity to a group identity and by whatever favor we show to the group entity, we are actually giving ourself egotistic pleasure.