I, too, find it disconcerting to join in with a tune at a session when I can't remember what it's called. Ususally it's fine, but sometimes when I do remember the name I realise an instant later that it's one I can't really play, because something untoward happens in the B part, or the section of the tune we're just coming up to. The names of certain tricky tunes are filed in a section of my brain, labelled "DON' unaware of the pitfalls ahead.

But just occasionally it works out the other way - I get to the end, find out what it's called, and think, "Hey, I didn't think I could play that!"

Marje