I don't know how it is for other writers, but a lot of my time is spent staring at the monitor considering my next word, sentence, or concept. I don't like this staring contest. The monitor almost always wins. I get even more frustrated, though, when I just type and type then erase it over and over. So being lost in thought seems to be the lesser of two evils.
My current staring contest is with middle of my novel Shattered Certainties. Initially I was doing so to re-write the middle so I could market two smaller books, but I've since found a publisher that wants long sf/fantasy novels. Problem is, the whole monstrosity is about 12,000 words TOO long. So while I'm re-writing, I'm also trying to shorten the thing.
Every change I make here in the middle is changing vast tracts of the end. Not bad, really, because the changes are good (I've found some continuity errors that would later come back to haunt me!) but this means I'm going to have to throw most of the second 1/2 out and start from scratch. I've done this before, I know "killing my babies" is for the greater good, but it seems so overwhelming. It's like being confident in running your 5k's and suddenly signing up for a half-marathon. You THINK you can do it, but never having done it, yet, you know it's going to be a lot of work.