Selflessness is one of those things that you start out intentionally embodying, and then over time the concept itself dissolves into nothing. Then you're left with just what's happening, unconditionally understanding.
I wouldn’t go so far as to say selflessness is impossible, but 100% of the most pro social people I know got there by believing open individualism in their bones. They think they’ll have to be you at some point and so they want your experience to be good