We’re all familiar with the terrible trope of action movies (and cop shows) where a guy takes a bullet, and then in the end of the episode, he has his arm in a sling, but he’s all better by the end of the movie / very next episode. In the really real world, people don’t end up with a little artistic bruising or smudge of blood or soot, and walk, run, and fight perfectly…acrobatically and dramatically.
They certainly feel it the next day, too, and it only gets worse as you get older, or accumulate more damage. (It’s not the years, it’s the mileage… and the years.)
Two weeks after the last ER visit, my husband was complaining to a nurse that he shouldn’t still be this limited and in this much pain. Said worthy looked him in the eye, and said firmly, “You’re over 60. You’re not going to heal like you’re 20. It takes longer!” (She works with cowboys, truckers, and all sorts of other stubborn old coots as you’re likely to see in North Texas. She’s worth her weight in gold, and also not inclined to coddle. At all.)
In Science Fiction and Fantasy, we often employ handwavium – healing spells, regen(eration), nannites, divine favour, what have you. And that’s excellent, when needs must, the plot drives, and it’s worldbuilt in. (Who wouldn’t go to the clinic if they could?)
…Actually, that last sentence is an interesting source of complications. Who wouldn’t? Why would they be unable to get there, or to use it? What’s it like to be a person with more consequences for every risk than those around you, and how does that change their plans? As Brandon Sanderson put it in his Second Law of Magic, “Limitations are more interesting than powers.”
Sometimes, it’s really fun to read a book that takes you away, makes you into a character that can climb the heights of Mars, or sail the Kon-Tiki across the ocean… and sometimes, well, there’s Miles Vorkosigan, who spends his entire life throwing himself full-throttle against the limitations of his body, his society, and every star system nearby…
And sometimes having a character be a bit banged up helps build that suspension of disbelief. Building in old injuries, scars, arthritis, and an increasing awareness of one’s own limitations and mortality counts as things that made King’s Champion well-received by its readers.
So keep that in mind, as yet one more tool in your toolbox, to throw at your characters and make them struggle, and really make that victory hard-won!