Where does the generalization that true artistry arises from morose emotions originate from?

Why does the generalization that artists feed on negative emotions persist?

Certainly many artists suffer, but it’s not universal.

I act and write. My experience has been that I produce better work when I’m stable and not when I’m hyper, manic, sad, or depressed. I wrote a series of award winning poetry when I was particularly successful at my day job.

So, why the insistence that artists have to suffer to create?