Everyone has pretty much covered hp, so...
Think of daggers as 'worrying' or bleeding weapons (I know, didn't spell it right). Unless you make a solid blow, like a critical hit, you won't get an instant kill (unlike massive weapons such as the the two handed sword, hammer, or pickaxe).
If I'm not mistaken, lethal dagger strikes are almost always from striking a vital spot and never from massive damage (crushed skull, etc). Your just going to have to wear them down. Most knife fights start as attacks to exposed hands and arms, then work up (or down, for those of you who play dirty...). The low hp could be because, in order to use the weapon, you have to slip in, jab or slice, then slip out of reach before they attack. Kind of difficult to land a telling blow in that kind of situation, and it only gets harder when opposing weapons get larger. Decisive attacks don't come until someone is massively incapacitated or makes a grievous mistake (generally happenes with them low level folk...). The longer you've been doing it, the better your odds of not bleeding out before the other guy...
