It happens to me the same. I think it has to be with our insecurities.
I can’t count the times I wrote a reply to a thread and decided to not post it because of many reasons.
For example, I didn’t consider that I brought anything helpful, or add anything to what it has already been said, or because it was too obvious (you know, these times you want to say to a person that you are there and that you understand him/her but you don’t feel that you have much to add to offer an effective help).

In relations to the feedback I may received in threads I open, I’m sometimes afraid of them to be judgemental but in spite of the fear, I see it as helpful because they make me think and maybe be more flexible about the topic treat.