It's not rocket science. Fear probably fuels that. It's comes from the same place as all my other control issues.
Claire, I think a lot of us are operating out of fear, at least initially. I certainly was. I think I've done a lot to address those fears, and in the process become less controlling. People on this board (including labug) have asked the right questions and when I think through and answer them, I come out better off. My IC has also been helpful. She has made me explain exactly what's going to happen if..... for instance, when I was so resistant to H moving out, she made me verbalize the ways my kids lives would be different. Turns out, not all that much. But it seemed like a huge thing in my head, until she forced me to say it.
What fears do you have Claire? Have you named them to yourself?