^^^^ There was a girl I went to grad school with that absolutely could not understand opportunity cost. Also I may or may not have been engaged to this person.
But anyway, she would spend hours upon hours, days upon days studying for every single exam, regardless of the difficulty. And me on the other hand would go all out for the challenging exams and then would ramp down my effort for the easier exams. That way I could actually rest my body and mind throughout the semester, making pharmacy school not that bad. She on the other hand was wound so tight and fatigued so bad, she was on the verge of a nervous breakdown quite often. And she also was neglecting her 3 young kids while chasing perfection which I wasn't so happy about.
But regardless of all that relentless effort, she was always ended up with like a 90 and I would walk away with an 83 or something. Now keep in mind, we are in grad school. That's it, you graduate and you go to work. A so-so GPA like mine got the same exact degree as her slightly better GPA. I knew that I just needed to pass and I would win the war. But at the end of the day, she probably took years off her life with all the stress and worry, constantly running at redline to get those few extra points.
Sorry, this got longer than I expected,
TL:DR Understanding opportunity costs makes a world of difference