Nicholson Baker famously built an entire book around the breaking of a shoelace. The result was The Mezzanine, one of the best books ever written about things. In Baker's case his left and right laces broke within a day of one another after two years of use. Noticing this was sufficient to bring on a state of near ecstasy in the writer.
"The near simultaneity was very exciting - it made the variables of private life seem suddenly graspable and law- abiding."
For most of the time, those variables remain slippery. Unless they have life-threatening consequences, the ways in which things fail is seldom discussed. Yet behind the doors of companies' engineering departments, the science of breaking down and wearing out has its own special vocabulary. The former more than the latter, in fact. Breaking down supplies an event, a point in time, something that may be measured. In a rare hyperbole, engineers use the term "catastrophic failure" to describe such a sudden occurrence, even if it applies only to the snapping of a rubber band. The crucial variable for such things as shoelaces or a rubber bands, which can fail in really only a single way, is its mean time between failures (MTBF) - the "between" is a bit of self-deception, implying that somebody might bother to repair a shoelace or a rubber band and start again as new, which we, in the real world, know never happens. In order to gauge the MTBF, the product may - with equal melodramatic gusto - be tested "to destruction".
What really induces Baker's rapture is not the simple fact that his laces broke so nearly synchronously, but the suggestion - quite misleading - not only that the MTBF of these particular shoelaces is known, but that what statisticians call the standard deviation from this average is negligible. In other words, we are led to believe that we can predict not only when one lace will break but that any other laces tested in the same way are extremely likely to break around the same time. (The near-coincidence is remarkable only if Baker replaced both shoelaces simultaneously on the former occasion, which is itself unlikely. In the book, Baker unaccountably fails to close this loophole.) This in turn raises the thought that if this figure really were known, you could plan ahead and enter the likely breakage date in your diary and so buy replacements before the originals broke. You can't, of course. You buy them and store them against the eventuality. Or, more likely, you are entirely unprepared when the Mezzanine moment strikes.
One domestic product does occasionally state a lifetime - the light bulb. It does so with an entirely spurious scientific accuracy that stems perhaps from its also having precise electrical ratings (240V, 100W and, think of a nice round number, let's say 1,000 hours). But even light bulbs don't blow with any meaningful predictability. Most products keep quiet about the fact that they will fail sooner or later, whether catastrophically or merely by erosion. Small items cost too little for people to care; large ones are too complex to provide estimates, because failure in one part can lead to failure of the whole. (What is the MTBF of a space shuttle?)
For other products, it can be hard to say when failure comes. Decline is gradual. There are soulless quantitative reckonings in the insurer's "fair wear and tear" and the taxman's "depreciation", but no satisfactory qualitative way of describing these processes. This matters because the graph of a good product's life should not be simply one of exponential decay from a starting high when the object leaves the factory in its shiny wrapping. Balancing the upward and the decay curve requires great judgement and skill in the choice of materials, the means of assembly and the finishes of a product. This is not about durability, which every manufacturer purports to understand anyway - durability is just a level graph. This is about maturing with age, acquiring a patina and understanding that, before a thing is worn out, it must be worn in.