Communication is the Bottom Line
For each person, how you communicate verbally and non-verbally tells everybody else something about you. Are you more verbally expressive or are you more the quiet type? Does your body language speak more loudly than your words speak? When you are happy, does it show on your face or do you just feel it inside and keep your facial expression 'in tact'? Are you a person who expresses through body language by reacting clearly to every thing and other people are easily aware of what is happening for you?
In the hands, there are many markings that each person has but one specifically, the heart line, which is the horizontal line closest to the fingers that begins under the pinkie, identifies your non-verbal expression type.
If it curves up and touches either the index or middle finger, then you tend to show how you feel through your body language and facial expressions.
If your heart line is straight and DOESN'T curve up but just goes across the hand from under the pinkie towards to the middle finger or index finger, then you are much more careful about body language. Expressing your feelings doesn't make you feel comfortable. People can't read your facial expressions because you've gotten very good, organically, at not showing how you feel.
Neither of these styles is right or wrong. They are what they are. And judging somebody else for not expressing like you isn't helpful. They are who they are and are being true to themselves.