How do you draw the line with compassion for characters?

[Galacticdefender]

Do it! It would be hilarious.

I used to be a warrior in an epic fantasy universe like you, until I took a wrench in the knee.

Skyrim memes aside, when I wound my characters, it is generally something quite major, and generally in an epic(ish) way. Writing a scene in which the main character goes down in a hail of bullets is generally more fun than writing scene involving hitting your head on a bulkhead. I use injuries to show character's weaknesses instead of their invincibility, although with antagonists it is often the other way around.

Wounds can also be an effective way to take one character out of action for a bit while you focus on another one. (I've done this once or twice)

 

[Warren_Paul]

Finally, there's such a thing as escapism. I don't think readers would be too impressed if instead of being stabbed, he slipped on some mud and wrenched his knee, do you?

Do it! It would be hilarious.

Joe Abercrombie did something like this to one of his characters in his First Law trilogy. Granted it was a little bit more serious than just slipping in the mud though was still rather amusing. The verdict is still out on whether the accident killed the character though or not, I'm suspecting the not...

 

[Anne Lyle]

Wounds can also be an effective way to take one character out of action for a bit while you focus on another one. (I've done this once or twice)

There's also the tactic of using a minor but temporarily crippling injury to slow down the party just when they want to be going fast, thereby increasing tension. A wounded comrade is a much more useful plot device in these circumstances than a dead one

(Note that I've ever used such blatant trickery *ahem*)

 

[Gumboot]

Characters? Pffft, I've wiped out entire countries when the story demanded it.

 

[Gumboot]

Finally, there's such a thing as escapism. I don't think readers would be too impressed if instead of being stabbed, he slipped on some mud and wrenched his knee, do you?

In Jack Whyte's "Camulod Chronicles" (it's technically historical fiction but it's basically fantasy) he actually kills off a major and pretty bad ass character by having his horse lose its footing on a slippery mud hill at their home, and throw him off. Worse, the POV character is absent at the time so he gets back after the fact and is only told about it.

It worked brilliantly.

 

[Varangian]

I think I,Brian hit the nail on the head ("You don't hurt characters because you *want* to - you do it because the story demands it.")

In short, I don't think one should ever separate themselves from their characters (even when the character dies, and unfortunately that happens). A good story (science-fiction, mystery-thriller, or heroic fantasy) should be a reflection of life, and sometimes life is tough. Sometimes good people die. One writer, whom immediately springs to mind, that could bring every day reality into a fictional situation was David Gemmell. I'm sure that he ached over many of the characters that died (like Druss for instance, which was probably the first main character he ever killed). Like I said, sometimes good people die.