Oh, and BTW, I'm not suggesting that everyone or anyone needs the "safety net" all, or even most, of the time. Just that when one is there it doesn't necessarily mean you're actually falling and letting it catch you.


One aspect of this discussion is especially interesting to me as an instrument player. It's argued that the use of books or lyric sheets interferes with eye contact with the audience.   Leaving aside the case of singing with one's eyes closed, what I find interrupts my audience eye contact is more often my having to look down at the neck of my guitar than my having to glance at a lyric sheet.   It's not so much a matter of whether I know the song or not. It's just that in certain tricky runs or when I play "up the neck," I haven't overlearned the guitar work to the point where I can forgo glancing at my left hand and the guitar.   Some very good instrumentalists look at their hands and instruments a lot while playing; some don't.
To me, what interferes with my performing as an entertainer and breaks my connection with the audience is having to check out where my left hand is.    But I don't see much hue and cry about how amateurish it is to not be able to play all your instrumentals without looking.