It's not hard to make something that works ok most of the time. It's much harder to make it work all the time or at least to know for sure when it didn't work. It all depends on what is at stakes: if your clocks are wrong, are you just mildly inconvenienced? Do you get a cached result that should have expired? Is it a security problem (are you accepting a certificate that has expired)? Is it a correctness problem (is the causal order of a database update been inverted by mistake)? There is a spectrum of severity of problems caused by clock sync, and whether the solutions are trivially solved or provably impossible (or anything in between) ultimately depends on what you're trying to do.