There are matters you can’t know until you know them. Then you can’t unknow them. There are some experiences that are difficult to fully understand until you have them. Then there is no going back.
I will know if my characters have had a parent, child or closed loved one die. If you haven’t suffered that type of grief or bereavement, you can find it difficult to understand someone who has. Characters can suffer empathy failure.
Recently, I think the same of having children. We all instinctively know that having children changes your life. But quite how completely and how pervasively and how subtly is a process that I did not fully appreciate until – of course – I had a child myself.