The dagger looks like a simple curved dagger. It has some engravings on it that are written in an ancient toungue. Translated they would say:
“None can know who they truly are until they look at themselves through the eyes of others. Only a foolish man sees himself to be something he is not.”
The Dagger was created by Diril, the enchanter. He considered himself a great thinker and philosopher. It was his belief that it was foolish to act unless you fully understand the situation. Ironically, he was later killed by a man that his discontented wife was sleeping with, although had he simply acted opon the signs that he had noticed, he might not have met such an end.
Anyway, during the time before he was murdered, he created this Dagger, to prove that acting without full knowledge could only lead to trouble.
The origins of the dagger however are lost. It is known that it was not made by the Gods, but merely by an enchanter. The text itself can be deciphered with a spell, but the actual language is known only by beings that are immortal.
Most people do not even know that the daggers exists. There are actually several in existance, however most are on some mantle some-place being admired as an amusing trinket. Those that are not make their way from person to person and place to place. Those who realize what it is toss it aside as another cursed piece of trash, and those who don’t usually do not live long enough to tell anybody else.
All that common folk know about it is the warning that parents give their children not to pick up things off the ground because you never know when they aren’t what they seem.
It seems that Diril’s point was made after all, even if it was in vain.
A simple curved dagger that turns the weilder invisible…to himself. He looks normal to everybody else, however he is completely unable to see himself. A foolish character might find the dagger and immediately try to start mischeif, however he would soon realize his folly.