Egotism without altruistic instincts is an exhausting mess of trying to calculate the long-run individual advantage of "being nice". Almost everything you do is iterated prisoner's dilemma, and you have to also understand whether to be rational or superrational.

Given altruistic insticts, there's actually no clear division between the two, because you do things because they feel good (egotism) and they feel good because they're altruistic (altruism).

However, it's highly advisable to develop reflexive altruistic instincts to the extent that you can. If I find out that you have no altruistic instincts and you're just biding your time until you can betray me in iterated prisoner's dilemma, I rationally ought to betray you first (and warn everyone else that you can't be trusted to care about anyone else, so always be on guard).

Unbounded altruism also renders one unacceptably vulnerable to prisoner's dilemma attacks, however, so you still have to do the superrationality thing to an extent. The point though is that if you are able to do it in general by finding a community of people whose personalities you trust (because e.g. they exhibit goodwill), it's a lot less exhausting than constantly doing the are-my-expected-future-interactions-persistent-and-reciprocal-enough-so-they-won't-betray-me-yet thing constantly.