[simias]

I think it's possible, but it becomes less and less likely with the depth of the latches.

Supposing your keyboard key input was latched by a flop and you pressed the key at the exact right moment you could violate the timings of the flop and have it end up in a metastable state.

That's why you usually put a bunch of delay flops when sampling such a signal in the hope that you'll manage to have a stable signal down the line, however that doesn't remove the problem altogether, it just makes the probability of the problem happening very low.

[schoen]

Huh, sounds kind of like probabilistic primality testing! (We can specify the probability of getting a false positive in the primality test and make it as low as we want, though it's still always formally possible to have false positives.)