[SixOfSpades]

In that case, Thuram, the problem was your THAC0. Just because you've Hidden in Shadows, moved behind somebody, and attacked them, doesn't automatically guarantee a hit.

Thieves and Rangers (whether they're trying to Backstab or not) get a -4 bonus to their THAC0 when they're in Stealth, but Thieves have lousy THAC0 to begin with. To compensate, always use the highest-enchanted weapon you can, and don't waste your time with weapons that you're not proficient in.

As soon as you attack somebody, you begin to come out of Stealth. If your Backstab doesn't connect by the third swing, run away. Go back to your shadowy little corner, slip back into Stealth, and try again.