"How are you?" is a nice question. It's a friendly way that people greet each other. But when a man says"How are you?", he hopes to hear the answer"Fine", even if his friend isn't fine. The reason is that"How are you?" isn't really a question, and"fine" isn't really an answer. They are like saying"Hello" or"Hi".
Sometimes people also don't say exactly what they mean. For example, when someone asks"Do you agree(同意)?", other people may be thinking, "No, I don't agree." But it doesn't sound very polite (礼貌的), so they often say, "I'm not so sure." It is a nicer way.
When you want to finish talking with your friend, you may say"I have to go now." Sometimes you give an excuse, "I have much homework to do." and so on. This is a polite way to stop a conversation and it doesn't hurt(伤害) people's feelings.
People don't always say exactly what they think. And it's a part of the game of language.
