They have been kept in silence by others not valuing or encouraging their thoughts or opinions. It is a way to keep them in their place. Oppressive silence becomes internalized resulting in a poor self-concept. Acquiescence is often the response - supposedly to keep the peace in the family or in the work place. It is not just the absence of talk.
Silence has substance.
It is the presence of something. Thomas Merton claims that silence is our admission that we have broken communication with God and are now willing to listen. We can be reduced to silence in times of doubt, uncertainty, nothingness, and awe. When we have exhausted all our human efforts, experience the limitations of human justice, or the finitude of human relationships, we are left with silence. Those who have experienced the sacrament of failure are more likely to know the emptying power of silence.