A few pointers:
1) The programming of society is geared towards guilt for being abundant. You may find yourself apologetic for being more succesful than those you spend time with. E.g. you degrade or refrain yourself from becoming selfishly wealthy because there are poor people obsessing that they are more worthy of getting what you could/are consciously attracting to youself.
2) Who do you give to and what? If you're giving money to men in poverty you are only making things worse for both them and yourself. Poverty is a mind-set capable/designed to disintegrate value and perpetuate despondency. Money is not the answer, wisdom and understanding have the power to eradicate poverty and its negative symptoms.
3) Resources are infinite. More to you is not less to others if and only if you are a man of creating more wealth and value, not if you are a man of wicked thoughts and abilities used to
mooch off others.
4) Selfishness is described as
concern with one's own interests, without reagard for others. A quick read may give the sentence a bad stigma, but
without regard for others is not equal to
doing harm unto others.
5) Self-sacrifice is a cause of low self-esteem. Imagine wives living in destructive relationships because they are programmed to adapt, cover for the abuses and roll with the punches. Or how about religions that tout that poverty and suffering is spiritual and we are helpless sinners to our very core. Poverty is a sin because it causes people to lie, cheat, steal and kill. The best you can do for society is to not be a poor person.
You may want to read something by Ayn Rand or Randy Gage to truly embrace how and why selfishness is a driving force for 'the common good'.