[burnished]

A simple example is clock timing in chess, you have to trust the client about when it received and when it sent if you want to avoid treating everyone as a cheater and penalizing genuine latency.

If I remember right an anecdote from someone in the trenches was along these lines for a more complicated real time game, though I think the peer comments have the more typical types of problems. I looked for the thread I was reading this in but came up dry, sorry!