sometimes you need to be more selfish

a therapist i know once told me that, except he didn't say sometimes. selfishness can get a bad reputation, but i'd like to give one example to show that it can be used as a force for good.

if you've ever let a driver out in front of you and not received a thank you wave, you'll probably have boiled with rage at the indecency of their behaviour. (they're no ken livingston but...)
However, if you thought of the whole interaction from a selfish point of view, then the reason you let them out isn't for them, nor is it to receive gratitude for your actions; if you take the reason for you actions to be for you, to make you a better person, or even just to feel good about what you have done, then their response is irrelevant.