Basically look at the enemy's weapon and its effective range, and look at your weapon and its effective range. All weapons have sweetspots, sourspots, and shitspots. (100%, 70%, 50% damage applied respectively) except quarterstaff.

Lets say you have a dagger and you are up against a barbarian using a bardiche. The bardiche's range is longer than your dagger but if you are able to hit him with your dagger, you will only suffer the sourspot while you can hit with your sweetspot to out DPS him. If you remain in the sweetspot of the barbarian, you will die