— Rita Mae Brown (often misattributed to Albert Einstein)
Doing the same thing over and over and expecting different results is also the definition of parenting. Kids don't learn on a smooth curve, they progress in stairsteps. The same child that acts out in a restaurant or has a candy tantrum at the grocery store will eventually stop, if you work hard to deal with those problems. In the mean time, you still go to restaurants and grocery stores because that's part of life. Each time expecting a different result, regardless of prior experience.
Eventually you get a different result. That's called growth.
Building a writing career works pretty much the same way. Otherwise none of us would survive our first handful of rejections. I had over three hundred before I sold a single story. Was I insane to keep sending out, and expecting a result different from continued rejection? Apparently not, though since that first sale I've had almost fifteen hundred more rejections, and almost three hundred acceptances.
Unless you're one of those rare people who can explicitly and consciously self-direct your learning processes (I'm certainly not, and off the top of my head I can only name one person who is), almost everything about professional fiction writing, especially in the pre-published and early-career phases, seems to fall under this rubric. You write drafts with flawed characters, critiquers and editors point this out to you, so you write more drafts with more flawed characters. Then one day you write a good draft where the characterization is solid. Your next handful are wobbly, then you get another good one. About then, the feedback you get shifts to complaints about your endings.
Developing as a writer is a game of pound-the-peg. And the peg-pounding part is a process of repetition with expectation of change. My advice? Be insane, just be insane with feedback and effort at self-improvement.