In any field of scientific endeavor, anything that can go wrong will go wrong. If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong. If anything just cannot go wrong, it will anyway. If you perceive that there are four possible ways in which a procedure can go wrong and circumvent these, then a fifth way, unprepared for, will promptly develop. If everything seems to be going well, you have obviously overlooked something.
Nature always sides with the hidden flaw.
It is impossible to make anything foolproof, because fools are so ingenious. Honesty is the best policy - there's less competition. He who hesitates is not only lost, but several miles from the next freeway exit. If computers get too powerful, we can organize them into committee. That'll do them in.