"I try to avoid extreme negativity about me or my ventures (and also extreme positivity). Both can burrow into your heart and paralyze you."
When I read that my first reaction was along the lines of "Huh. I wonder why extreme positivity would be so bad." But it actually only took me a minute or so to come up with a few possible scenarios.
The one that speaks most to me is that there's a risk in being too willing to listen to the people that give unconditional praise of my work. After all, if two people are talking to me about a story I've written and one says "Oh my gosh, it's the best thing ever!!!" and the other says "Meh. Well, I liked this and this but that and that need some work." then it's a heck of a lot easier to only listen to the first person. But there are plenty of times when that will lead to slightly lazy, slightly sloppy work going out on submission, which isn't where you want to be going if you're trying to succeed at the top-level markets.
But then again -- here's where it gets really tricky -- sometimes listening to the first person is the right thing to do. Maybe the story as written would be "better" than the story as revised to meet the second person's preferences. After all, every single story that's ever been written will have a certain percentage of readers who simply don't like it. I've seen stories nominated for major awards get absolutely shredded by readers. Not because they're contrary or "didn't get it" or anything like that. It just won't have hit their fiction-loving buttons.
So judgement is required. You have to know when to trust your gut and which opinions to trust when you're getting feedback on your work. And this ties back to the original statement, too. If someone is always positive about your work, if they just love every word you've ever written... Then they're not helpful as someone to provide feedback on your work because you already know what they're going to say.
Are there other ways than these that you've found praise for your writing to be damaging?