Writing is a lot like losing weight.
As you work toward your goal weight, you’ll hit set points along the way. You’ll stay at that set point for awhile then start losing again.
With writing, you constantly strive to be a better writer and then you’ll hit a set point. Breakthroughs in writing come in spurts. You’ll write the same way for awhile and then — Bam! — a breakthrough. You’ll improve by leaps and bounds and then hit another set point.
The difficulty lies in recognizing that improvement can still be made and where. The closer to perfection a writer gets, the harder it is to see that you aren’t there yet.
Another analogy comes from math — the asymptote. Basically, in order to get somewhere, you must get half way there first. And then half way again. This continues for infinity, so that although you get very close to your goal, you never actually arrive.
Writing is an asymptotic process. The writer forever strives for perfection — but there is no such place in reality, so the writer can never get there. But they can get pretty darn close.