Ever delete an email by mistake? Ever accidentally highlight a bunch of text and then press delete? Ever wish the iPhone had “Undo” like the Mac does? Of course you have, and of course it does (although it didn’t used to). All you have to do is shake your iPhone to get a box asking you whether you want to undo whatever it is you did. If the box doesn’t pop up, shake harder.
Advice: try it before you need it, so you see how it works.