Why?

Because you can spam hide and sneak, then use them in order to avoid many of the guys that would kill you. You also have mark of the prey for that one ranger or muter (assuming you can get it onto them without dying in the process -- but that's easy enough).

You have detect hidden and detect invis (the latter via the heightened awareness skill) in order to see enemies coming who might otherwise kill you. It will also allow you to see hidden and invisible mobs.

You have a skill that helps you save vs spells, and you tank well, plus you can vanish (teleport within the area) helping you to survive vs mobs and players.

You have skills that should turn almost any fight if used correctly. Kotegaeshi, for example, is very nice vs most melee people, and most spellcasters can't stop you running away if they get the upper hand.

Finally, you can attack people who don't know that YOU are coming, by attacking when they are hurt, or have lagged themselves out.