I changed a shoelace recently: a rather unusual if banal event. You see, one doesn't get to or need to replace shoelaces much anymore. In fact, I can't recall my last incident. (Of course, since I can barely recall what I had for any given meal yesterday, that isn't in itself remarkable.)
There was a time, however, when we were sure to keep replacement laces on hand because the unceremonious breaking-of-the-lace was not an uncommon event. Frequently, I'd be lacing up my shoes when a lace would simply snap in two, and I don't think my Samson-like strength was the cause of the mishap — it was all down to the material. Somewhere along the line, however, that changed. Now, we can own shoes for years, use them regularly, and the laces will most likely remain intact and reliable for the duration. Even in the case of the recent changing, the shoelace in question didn't snap; it simply frayed and weakened but held on, and I left it in that condition for quite a while before I got around to dealing with it.
I'm not sure when it all changed — when the miracle of the shoelace occurred. It seems to me that it might have been the late seventies or early to mid eighties, but I can't be sure. Maybe it wasn't even an overnight shift; maybe they improved gradually to the point where they seldom seem to fail; but, improve they did.
So, I wonder why, we still have to buy them in pairs.