When you hit the ruler it will nick the blade. It can also be the mat. You usually use the mat in the same place all the time. Try putting the mat in a bathtub full of room temperature water, and scrub it with a brush, to get any lint out. Then hang it up to dry or dry with a towel. The water helps heal the mat so you can cut, and not have to press down on the blade so hard. Hope this helps.