If it were only that simple. Problem is, I've seen it work just the opposite of that. Here's one example: There was a man (about 80 years old) who was suffering from extreme fatigue and couldn't do anything but sit all day.
His doctor diagnosed him with cardiovascular disease and told him he needed a bypass operation. Lack of blood flow was causing his fatigue. When I found out that he was waiting for a date to be operated on, I offered him another alternative. It was a diet to reverse his coronary artery disease. He went from being depressed to happy and enthusiastic about the diet. And it's amazing how fast he got results. Within a week he was feeling much better (no fatigue) and he was doing chores around the house. Within about 10 days he was doing his own yard work again, like cutting the grass. And a little while after that he was going out and playing golf.
This continued for about two or three years. But, sadly, he started to feel as though he wasn't having enough fun or enjoyment, as you have suggested above. So he went back to his former junk food diet to get more enjoyment in life. Within a short period of time his arteries clogged up again and his doctor told him he needed bypass surgery. So he figured, "I'll get the surgery and then I'll be able to continue my diet, assuming the surgery will keep me well for about three or four years until I die". Well, It didn't work that way and if I had known what he was going to do I would have told him. First of all, it took him months to recover from the operation. And then he started having neuropathy pains in his hands and feet from lack of blood flow to the nerves. That's because a bypass operation only focuses on one area, whereas blood flow issues are likely systemic. So the pain got continually worse and he went from using a cane to a walker and then a wheelchair.
So the bottom line is that he spent the last three to three and a half years in terrible pain. Instead of being happy, he was miserable the whole time. The foolish trade that he made had nothing to do with reality. Yet people do this all the time and even promote it to others as a way to have a happy ending to life.