>>24511356We don't know exactly how Epicurus arrived at that conclusion since his works are lost but going by Cicero's account (which is very unreliable because he hated the guy and constantly mocked his views), Epicurus introduced the swerve into Democritus' atomist system because he needed to justify free will, which he felt was self-evident, being included in it.
So his reasoning was likely something along the line of
>Free will exists, therefore there must be some fundamental aspect of nature that makes it non-deterministic.