It implies a high level of reliability and ease of use.
Here are some examples:
* "This recipe is foolproof, even a beginner can make it."
* "The new security system is foolproof, it's virtually impossible to hack."
* "The instructions were so foolproof, I couldn't possibly get it wrong."
While the word "foolproof" suggests something cannot fail, it is important to remember that in reality, no system or plan is truly foolproof. There are always unforeseen circumstances or potential human error that could lead to failure.