When we are young in our childhood we don't really understand what having boundaries means. When a child is between two or three and sometimes actually even younger one word that a child does start to use is "no". Before that a child will turn their head away, or may put a hand out in an effort to push away, they will do this even when being spoon fed something that doesn't taste good to them. A child slowly learns what boundaries means emotionally, but, the child doesn't have any language skills to communicate these feelings.

What I learned simply through experiencing flashbacks is that our bodies and part of our brain remembers our early childhood more than we realize. So, if a child had a hard time feeling safe it can predispose that child to possibly developing ptsd if something bad enough happens. Also, growing up in an enviornment where parents or siblings don't respect boundaries means that child can have a harder time with boundaries and may even consider certain types of invaded boundaries "normal" and that can create problems later.

We are by nature designed to learn how to navigate whatever environment we are introduced to and that includes the kind of human beings we are growing up with experiencing. Therefore, there are behaviors that may not be ideal or even healthy, but, when we are young we don't know that but instead we just learn how to navigate whatever kind of behaviors we experience or witness. We begin to think these behaviors are actually "normal". After all, we genuinely do not know any different when we are young children.

So, if it was hard to be able to say "no" and have that respected, it's reasonable to say this can be something a person may feel even as an adult.