My first experience with prosthetics was helping to design shock-pace leads for atrial defibrillators. You can build them to last forever - but they're going to become useless and encrusted in plaque after 5-10-15 years and really? By the time you've been fitted with an atrial defibrillator, statistics says you're going to be dead in ten. So you design for your product to outlive the patient.

My second experience with prosthetics was at the bioengineering lab, a career I didn't pursue. They were working on artificial skin, blood pumps, and a laser scanning technology to improve the modeling and fit of prosthetic caps. The skin "worked" by being fibers so small that immune systems didn't know it was there, which allowed the body to use it as a lattice for scar tissue. No nerves, no sweat glands, no follicles, scar tissue. And it didn't work great. The blood pumps were hard because if you compress blood it ceases to be blood and since blood is a suspension, not a fluid, it follows dumbly nonlinear empirical equations. The stump scanner? Yeah, the "science" of "how do we put a prosthetic on this person" is still 1 at a time, by hand, using wraps, and hoping the necrosis isn't too bad.

The third time I encountered prosthetics was with a guy who I worked out... next to (he wasn't exactly my lifting buddy) at the club whose C-leg flew off while he was jogging on a treadmill. We talked about it a little bit; he lost his original leg in Kosovo and he was happy to have it. But, he said, it was still a far cry from a leg.

We've had eyeglasses for about 800 years. But as soon as it became even vaguely safe, millions of people who can afford it will happily swap a pair of inert lucite on their face for having razors and lasers slice into their literal eyeballs to get rid of them.