When you're a kid, getting hurt is inevitable; you run, jump, fight with your siblings and wrestle with your friends. As adults, our play is usually more relaxing and less agressive, but I'm sure most of us still engage in some roughhousing with our significant others every now and again.
Just like our parents warned us as children, as soon as people get rowdy someone's likely to get hurt. And the physically closer you are to someone, the more chances you'll have of accidentally injuring them. To me, the only thing worse than hurting myself is inadvertently hurting someone else, so tell me, have you or your significant other mistakenly injured the other when goofing around?