why do people tend to hide their feelings

why do humans need to hide their feelings? It sounds very weird to me sometimes but not entirely cos' me, myself also do that time to time. But seriously i really don't understands sometimes, for example, you had that strong feelings towards that particular person but instead of telling him/her, you tend to hide the feelings towards them. If u care for that someone or you still cannot let go of them, you tend to lie to yourself plus juz to keep quiet and keep all the feelings to yourself. Why people do that? Is it because they're afraid of rejection or denial?

This matter happens to me and i really felt that it's so unfair while you simply judge a person by listening by other and u had some comment to put on but you can't say it out loud. No matter how hard that person wants to explain that they're not like that, they won't listen and they don't really care bout' what you want to say. Moreover, both parties knows bout the problem and it's like very hard to say it out sometimes, but either one of them does, the other sure deny that they had the same feelings.

By the time the first person loses the interests on him/her, only that time they'll try to express their feelings. It's a hard situation for the first person to decide whether to move on or continue standing there.