I never questioned the severity of this piece of piece of advice when growing up because I have a cousin who lost an eye doing just that when she was very young. She was (and still is last time I checked) 2 years younger than me, so this wasn’t some distant story, this happened during our childhood, so as kids we were like, “damn, this shit’s for real!”
Several years later, their house burned down because guess what her little brother was doing? Yup, they taught us not only the importance of proper scissor transport procedures, but also that if you really must play with matches, for the love of God do it in the backyard, or better yet the driveway where a neighbor might see you and yell at you for being a stupid kid, but definitely not inside your parents’ dark walk-in closet, but seriously don’t play with matches.