[kej]

The sorites paradox says that removing a grain of sand from a heap doesn't stop it from being a heap, and yet we can do that until we are left with a single grain of sand which is clearly not a heap.

Likewise, taking elements from many influences and combining them involves a lot of creative choices about which pieces to take from which influence while copying one thing exactly involves no creative choices and is just reusing someone else's effort. It's the difference between baking someone a cake or getting one from the store.