No one’s thinking of a break up with their lover when things are going well. That can apply to actual, physical people as well as to creative enterprises (like writing, or martial arts.) No writer, scribbling away, high on inspiration, stops to say “Actually, I think I’d rather be an investment banker.” It’s not how endorphins work.
We start complaining (and contemplating new career paths) when we struggle with the current one. When the fights never end, when the inkwell feels dried up.
The fact that so many of us are complaining about their bad days shouldn’t be discouraging.
It just means that you’re not the only one struggling.