Probability and faith
Let us first define determinism. Determinism describes any black box where the same input will always produce the same output. As a result it is not operating with probability as a factor.
Let us now define free will as a black box where the same input will not always produce the same output. Perhaps probability is at play. Or choice. Or some input we cannot observe that governs this making it seem like free will draped in determinism.
Consider thus: to claim a synchronicity, a coincidence cannot be random chance or probability. The claim made for one coincidence, swallows all coincidences and probability as a result. And this, by free will, a sequence emerges claiming yourself deterministic.
Free will draped over by determinism... A faith of something beyond probability. The input you cannot observe to this black box.
What follows is any belief system that believes in free will, places faith in probability. Places faith on the unknown key of your black box.
If you wished to be reductionist, you could collapse the free will and determinism argument to one about probability. A coin flipped, had equal probability so they say. But classical mechanics is deterministic so they say. But quantum mechanics is probabilistic so they say.
Chekhov's cat... Schrödinger's smoking gun: locked beneath the folds of the Black Box.