I really don't think watching death on TV or in video games can compare to the act of actually killing someone.

It might actually hurt, because you have people, like the OP, who think they're prepared to do it because of what they've seen at a distance in safety, but then when the actual time comes to kill someone (or after someone is killed) the shock of the act and the pure, harsh, unmovable reality of the situation is more of a kick in the gut than it would have been had you not come into it with the belief that it'd be some casual thing like it is in a video game. TV, video games, can not prepare you for the visceral horror of the reality.

And always remember, you do NOT know how you'll react in a kill-or-be-killed situation until you've been there. There are many people who find themselves unable to pull the trigger, even though they doubtless believed they could just a few minutes before.

That's just my take on it, though. Dunno.