There may be some few who can totally hide their real emotions and put up artificial countenance . But such hardened , or specific trained people are quite less and we may not be coming across them usually at all.
Many times we would have faced some situation when people read our mind even though we did not want them to know it. The opposite also could have happened- that we enter into someone's place and see some particular expression on their face though they struggle to hide and put up a normal appearance.
In almost every language there can be a proverb in Malayalam "Mukham manassinte kannaadi"-meaning 'Face is the mirror of the mind'
Close people like mother, father, spouse, close friend etc. can easily understand even the minute changes in our mind by reading our face,however we try to put up a normal face.
Non-violence is the greatest Dharma; So too is all righteous violence.
A face is the index of mind applies aptly to people who are good natured, have love and affection towards others. Observe the face of a mother whose infant is sick, the face of a father when he does not have money to foot the expensive school fees, grandparents who have to send off their grandchildren whom they see few times a year only. Such people with a genuine heart and a good mind display their emotions on the face instantly.
Similarly, many professionals are trained to be emotionless and also trained to read the mind by observing the faces
In general, when someone is worried, this trait will reveal on anyone's face.
Do what inspires you !!