Grit is hard to measure in quantifiable terms so I have my doubts about the methodology of the studies referenced here that are making claims about it. But that

Grit is hard to measure in quantifiable terms so I have my doubts about the methodology of the studies referenced here that are making claims about it. But that doesn’t mean it isn’t a good differentiator for relative success. That is, it may not be a perfect predictor of success in itself, but it is a contributor. And relative to someone with all other factors held equal, the person with more grit will be more successful. That’s not really controversial or in need of “evidence”, as it is self-evident.