Monism is the belief that everything is ultimately one (a belief that is central to Hinduism). You, me, animals, plants, nature, the universe – monism basically states that everything is one – that we are all one body and that all contradictions or differences are merely a result of illusion.
Now, for the sake of the argument, lets say that this is true – that everything ultimately is one. That there really is no difference between you and me, but that the difference we do perceive is merely an illusion. We are all one!
Okay, then technically by this logic, by doing what is in my best interest I am also doing what is in everybody else’s best interests.
If everything is one, then by helping myself am I not also helping others? They say we should ‘help others’, or ‘put others before yourself’. But if we are all one and the same, then technically it makes no difference if I act in self interest or for the ‘sake of others’. If we are all one, then by acting in self-interest I am also acting for the interest of the whole.