Because we been trained like that, not to express opinions in our childhood. What happened when you said no to your parents when you was little? Or you wanted something to tell, but you been shut up or ignored?
Look how many little children coming and telling something to adults, want to speak and adults pushing them to go away, don’t laugh loud, don’t speak, don’t…don’t…no, no,no many children hearing 1000 times a day. Also they hearing: “ because I said so!”
Not each time parents are wrong and they must draw boundaries as well apply rules and say NO to children. But it’s all about communication.
But if a parent was extremely dominant or parent who breached security of the child, left, threatened, abused, neglected purposely, it might be hard to say no to that parent now.
Just because of same fear to be rejected- security feeling will be breached.
Remember, second thing after basic needs is security feeling for children.
You must be honest even with your parents and relatives now. But most important be honest with yourself and follow yourself.