Quick thought experiment: would you tell a physically abused child, to their face, "Do you honestly believe your misery is a result of external consequences? Be grateful for what you do have."
Some people habitually blame things that they caused themselves on others. Others commit the converse and blame things other people did on themselves. I don't think either of these facilitates your mental health.
If you are an adult, almost certainly things happened to you that weren't your fault, but that are your responsibility. That's life. Life is the process of dealing with those things, and then you die. It sucks, but it's worth it. Am I out of platitudes yet?
All these habits are founded on a desire to be better, which in turn needs to be rooted, at least partly, in compassion for yourself. If you don't want to be better, because you don't think you deserve it, because you have had that beaten into you, why would you exercise or eat better? And the only way you're guaranteed to have compassion for you when you need it is to learn how to generate it yourself. You're not going to exercise or eat clean or anything healthy sustainably if you're sustaining it by abusing yourself verbally or emotionally. So don't do that.
So, for some, it can help.
This is a significant, non-scalable investment of time and effort in the well-being of another. It wouldn't surprise me if such experiences were in extremely short supply in those people's lives. From my experience, there's a significant chunk of the population for which this sort of investment is a required component for their on-going sense of self-worth.
I'm not sure why, but my experience is that tech culture is particularly prone to an almost axiomatic rejection of this aspect of human interaction and well-being, and often exhibits significant prejudice towards those for whom this external requirement for well-being manifests.
Some examples:
* treating all human beings as a whole, which allows people to share happiness on other people's achievement - this kind of resonates with the theory of Selfish Gene by Richard Dawkins, where it argues that the goal of all humans is to maximize the chance that the entire gene pool will continue to exist
* reduce sense of one's own identity - which helps people during hard times by thinking about how small one single person is compared to the entire race, maybe even the entire universe
And of course, there's the advocate around being grateful, being compassionate, do more meditation etc.
Some beliefs are so destructive that no amount of exercise will alleviate their effect. For instance, some people are what I call blamers. They believe that their misery is because of life, others, society... They refuse to accept what life has given them (whether their look, family...). They honestly believe that their misery is result of external consequences. No amount of exercise will fix that. Contrast that to those who are always grateful. Always glad with what they got. Happiness for these is simple.