IanB said:Because it avoids player conflict. More annoying OOC fights have been started in games I've played by people hitting each other with fireballs than any other single occurence I can think of. Second place is people hitting each other with lightning bolts. And don't get me started on 1E chain lightning. Also, subjectively, the game is more fun without it.
In our game, the PCs would be arguing over such a situation, not the players. And that is fun for some people. YMMV.
It's ok in your game for a PC to make a mistake with a trap, but to not make a mistake with targeting? It's ok for the PC Fighter to move out of position and the BBEG takes advantage of that to charge the PC Wizard, but it's not ok for the PC Wizard to make a targeting mistake? Strange.
Lots of bad PC decisions can injure or kill a fellow PC. It's not just targeting. Why protect from one type of mistake and not another? Strange.