Daggers were an excellent alternative to a larger and more cumbersome weapon such as a sword and in some places swords were illegal to carry unless you were a member of the nobility. A well made dagger was a viable alternative. Kept within easy reach, it could easily and quickly be brought into play if the occasion called for it. The highways and alleys of medieval Europe were no safer than today.
The cost of acquiring a sword was also a factor in the apparent popularity of daggers. Some daggers could be quite large, in some cases with blade lengths reaching 18 inches. Indeed a blade of this size held in a competent hand could be quite fearsome. Cinquidea daggers were often very large with blade widths of 3 to 5 inches and lengths of 12 to 18 inches. Even though less threatening than a sword, a well made dagger on your hip announced to one and all your intention to defend yourself if necessary.
Some daggers were quite ornate, especially those belonging to the nobility or royalty. Sometimes worn more as deadly jewelry, the finest examples are truly exquisite works of art. In contrast some daggers are quite basic and barely more than a blade and handle wedged together.
At best a dagger is a durable well made tool and weapon of last resort. Having two edges rather than one allows you twice the cutting ability and a good strong point let’s you punctuate any opinion with no uncertainty.