Who put that there?

I'm constantly tinkering with things I've written. I know they say "Writing is rewriting" but it can get a bit silly! Even if someone asks for the script of a play I wrote 20 years ago - maybe even something that's been produced by several different companies - I do a paranoid polish before I send it out into the world again.
And really, the best way to rewrite is after a distance of time. So much jumps out at you, which you didn't notice before because you were too close to it. Things you can't quite believe you missed! I'm not just talking about typos - clunky phrasing; things that don't make sense, or could have more than one meaning; things that could simply be better. Even if I'm writing to a tight deadline, I try to finish a day or two early so I can at least allow a little break from it before I come back for a final assault.
This repeated revision over time means, of course, that I know some bits of my work by heart - I've read it so often. But what's absolutely magic is when I come across something I've totally forgotten I even put there.
It happened today. I was going through a TV script - last paranoid polish and all that, before submission. Now this is something I wrote years ago, so I really do know whole chunks of it almost word for word without even trying. Then a year ago a producer encouraged me to bring out certain characters more. I thought I'd remembered what I'd added, but I haven't looked at it since I did it. Today - two or three times - I came across something that felt completely new, and it was utterly glorious. I was thinking "Wow, that really works! I wish I'd thought of that!" even though I know perfectly well I must have done.
I can't describe how exciting it was. The vast majority of the time, rewriting seems to be a process of reminding yourself how rubbish your work is - so these little gifts that (very occasionally!) pop up and bite you on the butt in a good way make it all worthwhile.