Update: I've been using the wrong side of a utility knife blade for probably a decade

I was cutting open a box of printer paper at the warehouse, and my blade just kept snagging. My coworker Mike walked by, looked at it for a second, and said, 'You know you can snap off the dull part, right? There's lines on it.' I stared at the blade. I always just used it until the whole thing was dull, then tossed the whole blade. I never noticed the scored lines. I felt like an idiot. I've been throwing away 90% of a perfectly good blade for years. What other basic tool thing have I completely missed?