As has been stated above, the knife needs to be razor sharp, check your knives to see how sharp they are first…
the most common informal sharpness tests are;
The Thumbnail drag; using only the weight of the knife, lightly draw the knife across your thumbnail , keep your thumb pointing towards the floor, at around a 45 degree angle or so, as you pull the knife across the thumblail, it should “bite” in and feel slightly “draggy”, if it slips off your thumbnail or feels smooth, it’s not razor sharp
The paper slice (draw cut); take a standard 8.5x11 sheet of paper, hold it so a corner is sticking out, and rapidly slash-cut through the corner of the paper, a thin sliver of paper should flutter to the ground, alternatively, if you’re not comfortable slashcutting paper, perform a simple draw-cut (pull the knife towards you), the weight of the knife should be enough to draw it through the paper
The arm-hair shaving test (BE VERY CAREFUL WITH THIS ONE); place the knife flat against the top of your arm, and very gently, once again, using only the weight of the knife, push the knife STRAIGHT down your arm, DO NOT pull to either side, or you will cut yourself, you want the knife to move in a straight line
if the knife is sharp enough, you will see your arm hairs POP off your arm as they encounter the blade, if you don’t pop hairs with the knife flat against your arm, try again slightly increasing the angle
once again, be very careful with this last test, as it’s very easy to get cut…
i have a Spyderco Delica 4 Wave that will pop hairs flat against the skin, it’s amazingly, scary-sharp
if your knives don’t pass these tests, then they will need to be resharpened, once you’ve got them hair-popping sharp, maintain them at that level with a “Crock-Stick” style “V” sharpener (Spyderco Sharpmaker or Lansky Crock-Stick), the easiest way to keep your knives sharp is to never let them get dull in the first place, a few swipes on the ceramic rods should be all you need to keep them Scary Sharp
the times i’ve made Maki rolls, i’ve found that when my “Sushi Knife” (Joan Chen Sushi knife) gets dull, it tends to squish the Maki as it cuts, when it’s sharp, the cuts are clean, my new Sushi knife though, is my H-1 steel bladed Spyderco Pacific Salt, H-1 steel is completely rustproof, and can be sharpened to an almost Monomolecular sharpness, the Pacific has never squished a Maki roll, as i keep it Scary Sharp…