Good question!

This is one I face regularly. When I repeat I do so on-purpose! It has nothing to do with the amount of material I can play. I can play for several hours without repeating.

At big festivals, I presuem that I will have 80 percent new audience at each of (normally) four shows. If I amplaying with a band, I map out the sets ahead of time and leave wiggle room for changes. I select the songs I wish to repeat for the entire festival - some twice, some three times - never all four, and then I place them in each of the sets in a differnet order and surrounded by new material.

WHY repeat? Because there are songs I wish to highlight for that weekend - my sets are always planned around the "conversation" I wish to have with an audience. I am there to tell my tales, and isng my songs for the weekend - I want to repeat some of the songs and tales. AND audience members always ask for some repeats.

At smaller festivals where I'm apt to have more repeat audience members, I stagger the repitition of songs. I repeat fewer and spread them out, play them on different instruments or even with different arrangements.

I never repeat entire sets. I always tell the stories from the top of my head - but if they have the same elements, those elements may get repeated.

Having said all of that - I am always mindful of the repitition and those folks who may have heard the song and/or story previously.

At festivals, there are certin songs that people expect me to play. They will ask for thsoe sonogs - they will tell me they are disappointed if I don;t play them. So I plan ahead. I list those few songs in that category, and space them out over the weekend.