Might be useful to ask a different question: What makes people happy? It's things like relationships, satisfying work, accomplishment. (and many, many more) Then the real question emerges: How many of those happiness 'sources' are made better by intelligence? What percentage? Relationships? Seems like no. Work? Also seems like no, lots of work doesn't make use of a high IQ that people enjoy nonetheless. Accomplishmen…
As I heard someone say, happiness is your reality minus your expectations. Smart people see more variables that could be changed, more components that could be modified, and are less likely to accept things as they are. This creates a false sense of ease by which reality could be modified, and thus higher expectations for the world around them. I suspect this misplaces happiness and contentment, but the two are also…
Less intelligent people may be asking you to step in front of a bus because they don't see the bus and you cannot convince them that the bus exists because they're looking in the same direction as you and they don't see anything there. They don't trust your judgement, especially when others who also have equally poor vision agree with them and side against you.
The majority of people have poor vision and so they see the same vague blurry shapes as each other. Because of this, they will often agree with one another and side against intelligent people; who are a minority.
Moreover, it's easier to form consensus over blurry/vague concepts. This is the principle behind fortune-telling. Intelligent people will tend to disagree about details. Because they can see much more detail, there are more contentious points to argue about. It's harder for intelligent people to form consensus.
Being intelligent is a source of unhappiness because it is isolating to not be able to discuss what you see with others. It's like living alone in a parallel universe. You can see lower dimensions but you can't communicate to anyone else about the extra dimensions that exist in your reality because they are incapable of comprehending them. Plato's Allegory of the Cave comes to mind.