great thread - some very game attempts to explain FIE - I can see, of course, if you have a guitar amp or an orchstra going in your ear, you might want to block that out, but that's not a 'tuning' issue, that's a noise issue. Perhaps for group singing, too; but, really, if you can't hold your line when somebody's singing next to you, a finger in the ear won't help - the fact is you have no business doing choral singing. And for the solo, unaccompanied folksinger (how many of those do you see anymore? who would listen to it?) it's ridiculous to suggest they do it to 'stay in tune' -- stay in tune with what?!? they are UNACCOMPANIED, for god's sake! they can sing in whatever key they like!

honestly, you old folkies. Time to let this one go.