A foolproof method, plan, or system is built so that it is certain to work — even if the person using it is careless or not skilled. People say it about recipes, locks, instructions, and computer steps. Though actually, speakers often stretch it: they want you to feel safe, but nothing in real life is impossible to mess up, so foolproof can be a boast. Neutral, everyday English. You will sometimes hear the verb too: to foolproof a process is to change it so that mistakes become hard to make. Putting it in front of a noun is the usual use.

萬無一失的。工廠和介面設計裡，把東西做成就算疏忽也不容易出錯，台灣也說「防呆」。