MHO: the myth is broader: that everybody gets more or less what he deserves. I have heard many times, justification of why person X is poor, pointing he is lazy, wastes money in alcohol, etc. but I have seen poor people, and is (typically) not the case. The problem is, when people is poor, there are no pleasures, often only alcohol is a way out. Only people who were there or had vey near people in that situation understand what is like to be poor…
OTOH, people think that rich people made it by hard working.
I’m not saying there is no correlation whatsoever. But there is much less than most think, and great amounts of luck playing a bigger role, including, but not limited to, where you were born, family, contacts, etc.
The belief in a just world is a collective coping mechanism that protects us from the ugly truth of cosmic injustice and the reality that the only justice we have in the world is that which we make.
Often the people who benefit from injustice are the very ones we've tasked with creating justice. It's easier to believe justice will appear on its own than to face the mess of making it ourselves.