For the past couple of weeks, my students have heard me tell them to "jump ahead" or "fake it" (i.e., "make it up) when they do a run-through of their festival songs for me. Those are really a musician's two options on stage when we have a memory lapse.
Musicians & Memory
Musicians young and old struggle with memory. I have a few students who are really struggling with it this year (we memorize in chunks). You may ask, “Why do musicians need to memorize their songs?” If you learn something “by heart”, you know it inside and out. You understand it on several levels and can perform it confidently – consistently. Plus it just looks good.