Even if you do get your To up you still have no hp as a mist elf wizard. You're vulnerable to instadeath by traps until like level 25+. It's the price you pay for having ridiculously overpowered magic. I once found a room of greater molochs in DH and levelled from 17 to 29. Magic missile kills everything, including yourself - at higher levels it goes so far and bounces so much that it's hard to NOT kill yourself with it.