There are plenty of errors in this, and you're confusing the four prongs, but I'll run with it for now, since it's good enough. If I am doing code autocomplete

There are plenty of errors in this, and you're confusing the four prongs, but I'll run with it for now, since it's good enough. If I am doing code autocomplete, and copying three lines out of your program, those three lines are exceptionally unlikely to be "substantial ... in relation to the entire work." Where you're confused is lots of places, but the biggest one is you're mixing up the prongs. Most of the reason your Citizen Kane example might work (it probably wouldn't) is Factor #1, character of use. Commentary and education are favorable. I can come up with examples where 0.002% of an original work would not be okay, but they're pretty contrived. For your benefit, a random link: https://guides.lib.utexas.edu/fairuse/fourfactor https://guides.lib.utexas.edu/fairuse/fourfactor Size definitely matters. It's not a hard-and-fast rule, but a factor.