The Gap
The dagger is the gap-finder, and the gap is the whole point. It is the second strike when the first has opened the line, the blade that fits in a coat, the weapon of the hand that is always free. The dagger does not win the argument — the dagger finishes the sentence that the argument has already made.
A journeyman dagger is an honest edge, cheap, fast, and the only blade that fits in a coat — which is the whole reason the dagger is the weapon of the man who is not paid to stand. A master dagger has the maker's name on the tang, and the tang is the part that takes the blow so the hand does not — which is the whole point, and the whole reason the dagger is the weapon of the man who has already decided the argument is over.
In the Hand
The dagger is the sidearm band's whole argument: the gap, the second strike, the hand that is free. It is the answer to the flail, the answer to the parry, and the question the long sword asks: what if the hand is the weapon, and the weapon is the one that is always free? The dagger's answer is: the hand is the weapon, and the weapon is the one that finishes the sentence.
"The dagger is not a weapon. The dagger is a sentence — and the sentence is the one that finishes the argument." — guild master, The Company