"Important" was a bad choice of words on Mark's part, since its a value judgement that is necessarily going to differ from person to person.. However, he essential gist of what he's saying is true. If you don't have kids, you can spend more time focusing on things other than taking care of your kids. I'm a dad and it does take up a lot of time and limits what I can focus on. My only disagreement is based on a personal value judgement of whats important; raising a child is the most important thing to me, but that's not a universal truth for everyone.