It's a normal greeting in many languages to say "How are you?" or the like. (Locally here it's often "are you okay?".) Since I have the odd tendency to believe that people mean what they say, and to not lie if avoidable, I've been long confused as how to answer that. The answer may be complex, or it may be negative on a bad day. And do people really want to hear about it?
I think not, generally. What they want, I think, is to show that they care (which is surely true to some degree or other) and to reassure themself that you are one less thing for them to worry about.
And of course they usually can't help you anyway if you're having a bad day. So in that case I've developed a kind-of solution which does not involve any lies. I simply nod and smile and say: "And you!" That seems to be perfectly acceptable.
I'm reminded, it seems a common idea that "Good morning" means "it is a good morning." But it seems obvious to me that it means "I wish you a good morning."