ADJ-GRADED (计划、机器等)十分简单的,容易操作的,万无一失的 Something such as a plan or a machine that is foolproof is so well designed, easy to understand, or easy to use that it cannot go wrong or be used wrongly. (计划、机器等)十分简单的,容易操作的,万无一失的
The system is not 100 per cent foolproof.
这个系统并非是万无一失。
I spent the day working out a foolproof plan to save him.