People can identify things hurting them, but not always correctly. But people also can blame personal failings on external sources easily as well.

It’s like asking why studies using self-reported survey numbers on penis sizes cannot be treated as the ultimate truth, despite adults surely being able to use a measurement tape or a ruler. There is a reason for why the average numbers on all those studies using self-reported numbers are always at least one standard deviation larger than the average numbers obtained from a study that wasn’t just a self-reported survey.