It is impossible to make anything foolproof because fools are so ingenious. Whenever you set out to do something, something else must be done first. Every solution breeds new problems. Two wrongs are only the beginning. If at first you don't succeed, destroy all evidence that you tried.
Success always occurs in private, and failure in full view.
Be sure to change the messages, if you want. This example will appear in our forthcoming book on JavaScript. Nothing is as easy as it looks. Everything takes longer than you think. Anything that can go wrong will go wrong.