Make no mistake most humans will exploit any glitches and bugs they can find for personal advantage in game. It’s just machines can exploit timing bugs better.
If you're using a typical PC (or $deity forbid, a phone) with a typical consumer OS, there's several sources of variability between your controller and the visual feedback you receive from the game, each of which could randomly introduce delays on the order of milliseconds or more. That "randomly" here is the key phrase - lag itself is not a problem, the variability is.