The other week I got someone to video me at the Club doing a song I wrote myself, to put on You Tube. I'd been over to Ireland the week before and sang it 4 times there in front of quite big audiences without having the words to hand. Anyway I sailed through the first two verses, came to the third, I couldn't remember one word, came back to me withing a few seconds but the video was ruined. Crib notes of the first few lines of a verse is usually enough for me. Visualizing the words like a story can help too.

But there are some people who just can't remember lyrics, and in those cases I see no shame at all in having the lyrics in front of you. Many well known singer such as Hank Williams and Johnny Cash, Jim Reeves too, if you see old concert photos, you'll see a music stand in front of them.
I've seen a wee bit of folk snobbery on here saying you MUST learn the words. But I've seen those same types in folk clubs, including ours, variously forget words and insist on starting all over again, after already wasting time tuning up, and I find that spoils their performance all the more