...to the extent we can distract ourselves with little trifles, materialistic possesions and so on. To the extent one can be happy by constantly distracting themselves in such ways, that person can see more reason to be more totally selfish.
To the extent one loses their myopia and sees the bigger picture and sees how relatively meaningless yet another restaurant, another car, another outfit, etc, etc is, one has to turn elsewhere for meaning. And often here, is where people decide to be relatively altruistic instead. For whatever reason, many reasons perhaps.
To lose one's myopia often leads to being less selfish.
Just don't completely lose your myopia. As eventually all meaning is lost.