Writers are - and writing is - I think, intrinsically bipolar ... not in a clinical sense, of course, but as a necessity of the craft and business. The euphoria we have when the words flow perfectly and everything comes together is the high we remember when we stumble, freeze up, come back to yesterday's page and think, "This is all garbage." We need that negative impulse when it comes to editing, tempered with a little love. We have to simultaneously be our own worst critics and our own greatest fans, and somehow know which applies in which moment ... and, of course, we never get it right all the time.
The submissions process sets up another series of highs and lows. The acceptances, the rejections (far more frequent!), the comments in praise or critique, they all keep the rollercoaster going. Personally, I think there's nothing more frustrating than a rejection letter that has only positive things to say! If there was nothing you would change about it, why didn't you buy it?
Sadly, it often seems that growth and improvement as a writer comes as a greater ability to analyze your own flaws. As you get better, you only get harder on yourself. I look back at some of the whacky, unfiltered drivel I wrote when I was younger, and I miss that hyperactive energy. I wish there was some way to combine the blind passion of then with the discerning eye of now.
I also miss the teenager who thought, "I don't want to wait until eighteen to have my book published; that's arbitrary and silly." (And I would have used the word arbitrary; I was always a weird and wordy little kid.) Oh, how I miss that confidence. Now, that blithe assurance has been replaced by compulsion: I keep writing because I have to. Because of that tiny voice that says maybe, just maybe this time ...