I think it's mostly the shape of that curve. Why does it hit 80% gain at only 20% effort? Is that the same across many different tasks?

I'm a writer (novelist), and it's a common statement in writing circles (the ones I'm in, at least) that every writer has a million words of crap to get out. That's a rough estimate, of course, and I've always taken it to show that you have to work hard at your craft to improve. At an average of 1k words/hour, that's a good thousand hours of nothing but writing to get out.

Is that 20% effort? 50% 80% How does one chart or measure that?