If you design a product that lasts forever and you intend to build a business around that product—you want to sustain production of it, but also want to pay your own bills, your employees' paychecks, and other such expenses—you quickly run into a numbers problem in terms of available customers; there are only so many people on the planet, and far fewer who will be in the demographic that wants or needs what you’re selling.
Some products (lightbulbs and toothbrushes, for instance) have a massive potential customer base, but most are far more finite (and yours likely isn’t the only company angling for customers in any particular product niche). Thus, essentially all products are dependent on future purchases to sustain the businesses behind them: it's not enough to sell just one toothbrush to someone, nor is it enough to sell just one car, toaster, or laptop.
Even selling one toothbrush to every person on the planet wouldn't be enough to keep a business functional for very long: that forever-toothbrush would eventually see the shutdown of the company that made it after the profits from that initial round of several billion sales dried up.
The economic solution for this problem of needing to sell more things to more people, including previous customers, is often called "planned obsolescence," which means building a ceiling on utility into a product from the beginning so you don't risk running out of customers.
That toothbrush, then, will last a month or two, not forever.
The laptop you're using will probably last a solid few years before the components in it begin to show their age (and the software you want to run becomes a little much for it to easily manage).
Even the building you're living in will have components that are not meant to fail, but are meant to be replaced or substantially repaired at a semi-regular cadence.
There are practical reasons for this type of planning beyond the dollars-and-cents concerns of running a business.
Keeping costs low is a fairly fundamental concern for businesses and customers, and a forever-toothbrush might cost way more than any of us would be willing to pay (at least not if there's a non-forever toothbrush available at a fraction of the cost right next to it on store shelves).
While it might be possible to build a forever-toaster and forever-computer, then, it might not be practical, both in the sense that few people would be able to afford these products, and in the sense that the company making them would likely go out of business—which in turn could impact the "forever" proposition as repair services and replaceable components would likely cease to be available, post-bankruptcy.
While some elements of planned obsolescence are perhaps necessary (under our current systems of production and economics), however, there's another facet of this same concept often called "perceived obsolescence" which refers to our perception of the things we own rather than their actual utility.
Clothing arguably has a far longer functional life than many of us take advantage of, for instance.
In some cases legitimately bad clothing construction makes repairs and continued use inadvisable and tricky, but in other cases we're swayed not by some waning utility of the product, but by the artificial introduction of new "seasons" of clothes, new styles and trends that make us feel as if the products we own are no longer good or useful—at least not to the same degree as before.
The same is true of consumer devices like smartphones which have a surprisingly long lifespan in some cases, but which are often discarded or traded in long before they cease to function.
These trade-ins are generally less about a substantial drop in utility and more about wanting to have the newest, flashiest, whizbang version of said device (though in some cases our motivation is stoked by the introduction of new capabilities and software, both of which are unavailable or don't work as well on our older devices, even though they continue to do what they've always done at roughly the same level as before the new models were released).
This type of obsolescence is driven by comparison, not objective assessment of utility. And while this is an excellent means of keeping customers coming back for more products in the future—which is great for business—it can be an expensive cycle for customers, while also generating a lot of waste, which is less than ideal for the environment.
Some businesses are developing closed-cycle production mechanisms that should help with some of those waste issues, but our perception of what's functional, what's discardable, what's good and what's bad will continue to be informed by the marketing materials feeding these perceptual adjustments even if the ecological side of this model is solved.
Brain Lenses is part of the Understandary portfolio of projects.
You can find the Brain Lenses podcast at brainlenses.com or wherever you get your podcasts.