Retractable blades were the first major utility knife safety enhancement. When you're in the middle of a project, it's convenient to leave your knife's blade exposed so you can pick it up and use it immediately. But when (not if) you get interrupted or leave for a break, it's just as easy to forget and leave that blade exposed. This leads to accidents. A retractable safety utility knife solves this problem by automatically retracting the blade when the knife is not in use.