One way I have said this is "Everybody is always selfish. Some people just have a larger sense of self". That is, your self may cover your family, your tribe, your city, your nation, your planet, or even all life.

Brilliantly put.

It put me off guard when a friend of mine suggested that those who act towards others do so to gain self-esteem or an appreciation for themselves in their own eyes, implying that acting towards others is inheritently bad, for you're as if serving others with that. At the time I had the idea of altruism being separate from the self: I thought that people could either act towards others or towards themselves, or, to put it more precisely, to work towards others' pleasure and comfort or their own. It's interesting to see this idea fall apart: we do act selfishly when we help others, but it may result in benefit for others, from which we reap pleasure of self as well.

Now, I'm not saying it is reasonable for everyone to act in what the manner would be if everyone worked for the common good.

Why not? I understand that it's impossible in the way we picture ideal, but why not strive for it - that is, to help others either rather than or as well as yourself?