For what it's worth, the way I always think about it is like if you were running a marathon.
You're not winning. There's some dude up front who's clearly going to win. So while you're going along you shout up to the guy in front and say "Hey, buddy, what are you doing? You're up there thinking about yourself when there's that guy in the back who twisted his ankle and is limping along just trying to finish the race? Maybe you should slow down or go back and help him, huh, you disgusting selfish asshole?"
Because the guy up front possesses empathy and considers how he'd feel if he was the one who was injured, he thinks "Jeez, that is pretty terrible. Maybe I should slow down to help the poor guy? What if I am being selfish?"
Meanwhile as that guy's distracted and questioning himself, you run past him while laughing at what an idiot he is and finish in first.
It's all born from a desire to convince people that those stronger than you should feel guilty for acting in their own self interest, which is especially effective these days because with how chaotic the world is and how distant people have become everyone is more uncertain of themselves than ever.
The important part to remember though is that contrition and self-sacrifice will in no way guarantee the same in return when the situation is reversed; the only thing it will lead to is you being taken advantage of and left to rot, so you may as well keep going and tune out anyone telling you to feel bad for pursing your own interests.
