Expressing emotions

Why do people sometimes try to hide their emotions? Does control make you stronger, powerful? It's in the human nature to feel and to express emotions. When you're happy you feel like sharing your joy to other people. When you're sad you want to be lonely but yet you need someone to talk to about your problems. In some situations people control their emotions very well. These emotional boundaries appeared with the development of society. For example a teacher is not allowed to scream at the students even if he is very angry at them. A manager or a director has to smile and to be polite to all customers or clients even if sometimes he feels like 'killing' the other person.
Expressing emotions is also a cultural matter. Nations have different ways to display emotions. In my country, in Romania, people use a lot of gestures when they talk as well as different voice tones and touching.

When I arrived in Holland I was surprised that people who are extremely friendly (they smile and they try to help you with everything) are somehow a little 'cold'. It's just a personal impression but it might be a standard dutch way of acting.
The stress from work sometimes makes people control their emotions even in front of their friends. I'm not saying is bad to hide how you feel it's just not natural.
I'm a person that enjoys every moment of life. I love to laugh when I'm happy and I cry when I'm sad. But yet I moved to another country where I'm a stranger. I'd like to care less about what others think about me showing my emotions in public.