No act ever is completely novel.
And no act can ever be quite accomplished without variation.
In every act, fidelity to the model and departure from it
are inextricably mingled
in portion that ensure recognizable repetition,
together with such minor variation as the moment
and the circumstances allow.
When variation from the model
exceeds the amount of faithful copying,
then we have an invention.
George Kubler
in The Shape Of Time