To be honest.. I think everyone has.
I was performing this song with my friend like, yesterday, and I kinda had a mind blank and forgot the lyrics. I knew them already.. but I think I was either too nervous.. or I just. Idk, I probably got a little shock attack and blanked out. Sometimes, in a test I can forget the method and that ruins the whole test. For you, since idk you, let's just say maybe you forgot your lines in a play, or maybe you forgot your homework for the 10th time?