I always thought that a car was a reasonable metaphor for a body. You give it fuel, it runs reasonably well, and when parts occasionally break down you go to the repair shop and get it fixed.
As I get older, I realize just how wrong this metaphor is.
With a car, you can actually get things fixed. It may take several trips to the shop just to figure out what the problem is, and you'll probably replace several other perfectly working parts and send your repairman's kids through college along the way, but you can eventually nail it down and either repair or replace the broken part.
Also with a car, you may have things breaking often and feel like the repairs are never-ending. But you can fix things one by one and, when you're all done, start fixing them again until you finally reach your limit and torch the heap outside your home and try to bluff the insurance company into believing your story about the unfortunate accident with the squirrel and the M80.
A body, on the other hand, consists of parts that, when broken, never actually get completely fixed. And until the glorious future of black-market doner banks where you can get entirely new limbs and organs for the right price from the wrong people, you really can't replace what you have. Or even if you could, the things wouldn't actually fit and function correctly.
The model for body repair is: you go to the doctor, they give you some medicine and exercises, and you go away and work on the problem. Months of physical therapy and several stages of addiction later, you realize that, in fact, the problem is still there always will be.
If cars worked like bodies, we'd never actually get them fixed; we would just learn to make do. You've got a problem with a wheel? Learn to drive with three. Transmission problem? Just put it in neutral and give it a good shove when the light turns green. Heater won't shut off? Just strip down to your thong whenever you get behind the wheel. Meanwhile, your mechanic will give you some useless fuel additives and stretching exercises for the vehicle. Sure, they don't do any good, but it got you out of his shop and your money into his bank account. At least, unlike body repairs, it didn't cost you an actual arm and a leg.
With bodies, the trick that makes it all work is that another, worse problem eventually arises. You worry about your blood pressure until you blow your knee out. Then you go through therapy and surgery with your knee until shoulder tendonitis kicks in, and you go back to the doctor and get meds and exercises for the new problem. This new problem will be your main worry and time drain until the next part breaks, and so on, until some problem is dire enough to ground you, six feet down.
Meanwhile, you'd better watch out for your spouse. When they get sick of your constant moaning about your aches and pains, they may just decided to torch you some night and try to bluff the insurance company.