Children express what they feel and what they want through their actions, emotions, signals, and, by their second birthday, words. Then people respond, including their parents, teachers, and other children; responses can be active or passive, verbal or nonverbal, positive or negative.
These interactive episodes are usually brief, so there are a lot of them each day. For example, from multiple studies, a reasonable estimates that a typical toddler has his or her wants thwarted about twenty times an hour, or on an average of once every three minutes.
Whether it’s called for or not, each thwarting is a communication, a message, to the child: “No.” Then there are other messages: parents who come to a fussing baby in the middle of the night, children at school who let a new kid into their group, people who listen when you’re upset: “Yes.” Added to your personal experiences are the ones you witnessed: what happened when your siblings (if you had any) expressed themselves, and other children, and adults – and characters, real or fictional, in books, movies, and other media.
This learning about self-expression continues into adulthood and to this day. Throughout it, your brain’s negativity bias has highlighted episodes when self-expression led to painful feelings. The pain could be quite subtle, like mild dismay when a person’s eyes wander away while you’re speaking, or quite intense, like being spanked for mouthing off at a parent. In neural networks, the types of self-expression that led to pain became quickly associated with fear, and then with rewards like relief when you learned to inhibit them.