On the right track, but on the wrong lane

I quietly crossed the milestone of changing a thousand nappies. I could not pinpoint when that momentous event occurred, but I must have done so because I have been changing a nappy once a day for no fewer than 5 years. I could say I am a confident nappy-changer. But pride goes before a fall, and those who are exalted shall be humbled. For somewhere around nappy one thousand eight hundred and thirty-three, I made a mistake. I am not sure the mistake was entirely my own.

Disposable nappies have the concept of “front” and “back.” According to the ancient wisdom of nappy-making, the crafter would place a label on the back side saying “back.” I have always depended on this label for my nappy-changing. One day, however, my wife bought home a new brand of nappies. Unbeknownst to me, this brand had violated the sacred custom, and instead of labelling the back side “back”, it labelled the front side with “front.” Alas, this innocent change was the cause of my downfall. For when I incorrectly put the nappy on my toddler, the “front” label was on the back side and I had no visible sign of my error, having no “back” label to alert me of my mistake. Because of this, on my one thousand eight hundred and thirty-third attempt, I put the nappy back-to-front.

It is fair to say this experience is not uncommon. For our local highways are not made solely out of positive green signs that tell drivers where to go. At key junctions and at frequent intervals, there are even larger, bright red, signs on the other side which say “Wrong way. Go back.” The reason for this is obvious. If there were only positive signs, the unsuspecting driver would be left oblivious to their error (as I was with my nappy), until it was too late. As I used to say to the math students who asked me “Am I on the right track?” My frequent response was “Yes, but on the wrong lane.”

In my line of work, these sort of mistakes are called silent errors. A core principle says that no system should be designed such that an error be left unnoticed by a human. In the world of computer systems, as well as in engineering, and in medicines, where errors are a matter of life-and-death, this principle is vital.

The importance of prohibiting silent errors was clearly not enforced in the nappy industry or we would not have a brand that foolishly replace the negative “back” label with the positive “front” label. However, we should not hold it against them. The principle is much harder to apply than at first sight. For the designer of such systems must have a clear idea of all the possible errors that may occur in their complexity, and have the judicious wisdom as well as discipline to catch these errors before they are too late. This foresight requires a wealth of experience and a deep acquaintance of first-principles.

It is already difficult to discern mistakes in advance. We have an additional difficulty in our everyday life when we work with people different to us. What we think of as right looks right to our eyes. But we do not see what looks wrong to us look equally right to others. When we propose a new idea, we feel our job is done after we have articulated our point-of-view. And yet we are surprised to find that our family and colleagues stubbornly persist in their error. The reason is that, like the nappy without the “back” label, it does not occur to us that what is the opposite view still looks very sensible to others.

These days whenever I change the nappy, I cannot but wonder what else we are getting wrong. What if we were looking at our world in the wrong way, like peering down the wrong end of the telescope? If we have the reverse view of the universe, like the reverse side of the nappy, who is to tell us of our error? Would we be continually self-affirming in our mistake? If humanity in our sciences and social sciences and philosophy were to be fundamentally wrong in our view of the world, is there a prophet who, like the bright red sign on the highway road, that says “Wrong way. Go back.”?