I think the idea of positive thinking is an over-reaction to overly-negative thinking. If someone is depressed and thinking "I can't do anything right" then some attempted positive thinking would be a good idea (if possible). But if you're already pretty realistic then inflating that pushes what your thinking into delusion-ville.
Hypomanic people have unrealistically high self-esteem and optimism, and they get into loads of trouble because of it (like debt, "I'll just make more money later, no problem!") so there definitely is such a thing as pathological optimism.
From Skeptic magazine:
Positively Misguided:
The Myths & Mistakes
of the Positive Thinking Movement
by Steve Salerno
My college football coach was the kind of guy Stanley Kubrik must have had in mind when he conceived the over-the-top drill sergeant for his classic Vietnam film, Full Metal Jacket. During one game midway in my sophomore year, my offensive-line cohorts and I were having trouble opening holes for our ball carriers. Coach pulled us aside at half-time and lined us up against a wall. He then walked the line and — from a distance of maybe two inches — screamed into each of our faces in turn, “I want you to tell me now, are you ever gonna miss another block!?” There was a pungent Anglo-Saxon gerund between another and block, but good taste compels me to omit it.
The only acceptable answer was “No sir!”, which we too were expected to scream at ear-splitting volume. This would assure Coach of our mettle, dedication, and worthiness to have him browbeat us for the rest of the season. But to me, Coach’s question sounded unreasonable. I still had two-and-a-half seasons of football ahead of me. What assurances could I give? And so, when my turn came, I drew a breath and said, “Look, Coach, I certainly don’t want to miss another block! But probably yes, I think I will miss a few. Now and then.”
From the bewildered look on Coach’s face, you’d think I’d just morphed into a six-foot-four-inch wombat right before his eyes. For a moment he just stared at me. Then he exploded. Labeling me “a smart-ass” who was “out to show him up,” he banished me to the end of the bench. Not long after play resumed, however, he quietly inserted me back in the game. It seems my replacement — one of those players who would “never miss another block” — was missing quite a few of them.
There’s no mistaking the allure of an outlook in which you’ll make every block, get every job you apply for, close every sales call, and win the heart of every man or woman who catches your eye. This became clear to me many years post-college when I began research for a book about the human-potential movement. I quickly realized how invested Americans were in their optimism — and how irate they’d become at being challenged, or even just questioned, on it; I was encountering what essayist Barbara Ehrenreich, writing later in Harper’s, would bracket as “pathological” hope. It’s a world-view that’s seductive and uplifting and ennobling — all of that — and yet, evidence and common sense suggest it has nothing to do with setting (and implementing) realistic goals, establishing (and observing) priorities and, perhaps most important, recognizing valid limitations and obstacles.
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