There are two issues here: What you should tell yourself and what actually is. I read a sports psychology textbook which quoted a study or studies showing that

There are two issues here: What you should tell yourself and what actually is. I read a sports psychology textbook which quoted a study or studies showing that folks who concentrated on improving themselves and not worrying about the competition were winners. A long distance runner should care most about beating their own time. But note that in focusing on themselves, they end up winning. There are many areas of human effort. Some are more competitive than others. The post that this one claims to be refuting was specifically about competitive fields. Surely we can agree that some fields are competitive? Then the question is, in these fields, where winners abound (people focusing on their own efforts), are outcomes actually improved by the principal or executive investing more work. Although the voting patterns in this forum don't appear to agree, this is basically settled both in science and commonsense. It almost appears that people are conflating the issue of whether it's a good idea from a quality of life perspective with whether it works. Those are separate issues.