I had an interesting day. I was in the studio with a group of musicians, who shall remain nameless, and I said to them "Our exercise today is not to use 'undo' at all. So, there's no second takes. Or, if you do a second take, you have to do the whole take. There's no sort of drop in, change that little bit". The session broke down in, I'd say, 40 minutes. It was impossible for people to work in that restriction any longer.
Brian Eno