Unhappiness

It is still unclear to me what 'unhappiness' does. In general there is some notion that unhappy cities are less productive. But why exactly?

Is it simply that an unhappy citizen doesn't work a tile?

Pretty much, but if you get rampant unhappiness your city is kind of a waste as it costs the same maintenance and food, yet has people doing nothing.

Sounds like corruption with some adjustments. Hopefully unhappiness can be dealt with in the known ways of spreading happiness. My major gribe with corruption was that there was no way whatsoever to lower it. Build a court house in some city 20 tiles away and you get a 2nd shield and that's it. Making the unproductivity a part of unhappiness is a good idea.

It worries me too as in civ 3, at least unhappy citizen is still working. We can have a city with 6 happy and unhappy citizens in our city without any riot and still productive. If unhappy citizen is not productive, then would it mean a city even your capital is not productive ? Using the example above, 6 happy citizen in the capital will always be productive. Alas we have 6 unhappy citizens which doing nothing but adding fat to their belly! What a waste! So this means without enough food and happiness, even our core cities are not productive especially in the early stages where we are still building our empire. There goes to any wonder cities too.

Just my thought. I hope it`s not.

Think of it like an unhappy citizen is an entertainer, since that was the short-term instant solution to unhappiness in Civ 1-3... So just imagine those unhappy citizens taking time off to entertain themselves.