Writing Mathematics in Pencil, and Why Analogue Is Not Dead (2017)

There is also the old question of why mathematicians tend to prefer pencils over pens. The most common reason I've heard is to make correction easier, but I don't think that's the real one. When I'm doing math, I never erase, I just cross out and work around it because it's just scratch paper anyway.

I think the real reason for using pencil is the freedom to forget about it. With any type of pen, after a period of inaction, you have to fiddle a bit to get it writing nicely again. A pencil is instant, no matter how long you held it poised in air, pondering your next mark on the paper.