So there’s this moment in the play Julius Caesar where one Roman nobelman says to another, “The fault, dear Brutus, is not in our stars but in ourselves, that we are underlings.” And in the context of the play, that quotation makes perfect sense—these two guys did not suffer some unjust destiny; they made decisions that led them to their fates.
However, that quote has since been decontextualized over and over and used universally as a way of saying that the fault is not in the stars (i.e., fate/luck/whatever) but in individual people.