My biggest destructive habit when writing is my need to get it right. I really don’t mind if a scene is “right” or not because “right” in writing is relative. What gets me is the details. My stories tend to involve a lot of research, and I’m a stickler when it comes to getting those little things write.
I could be in the middle of a fast paced pivotal scene that I’d been planning and waiting to write all week, but if I come across a question that I don’t know the answer to I’ll stop dead in my tracks and go into research mode. For each book I work on I have a tub books on the subject and if I can’t find my answer there I’ll continue my search online. However, even once I find an answer I don’t feel comfortable using until I’ve gotten the same answer from at least two other sources.
For example, last year I was wrapped up in writing a scene in Entwined where the MC, who was a white Bengal Tiger at the time, was purring. The scene was going great, but then I started to wonder if tigers actually purred or not because heaven forbid she come off with the characteristics of a house cat instead of a tiger. Of course then I had to stop and go find out if tigers purred, which it turns out they don’t.
In many ways it’s a helpful destructive habit, but it’s still a destructive habit.