Why the Pretence?

I wonder why some people always say they are OK when in actual fact, they are not. 

I don't know why some pretend they understand everything but in reality, they don't capture anything. 

At other times too, they act like they are busy but in reality, they are lonely. 

Also, some people convince others that they just want to be friends, but what they really want is more than friendship. 
It baffles me when a guy or girl knows that the person they love has someone else but still pretend it doesn't hurt them, when it actually torments them inside.

Some people also pretend they've moved on, but the truth is, they still waiting. 

Finally, what confuses me the most is when somebody say ''it's over with him or her'', when in actual fact, they mean the opposite of they say. 

I just can't imagine what keeps some people from feeling free to express their exact feelings. Whatever the case may be, I believe one needs not pretend because life is like an ice-cream; we need to eat it before it melts.