I think there is a difference between the peaks of happiness and finding joy in contentment.
I see happiness as a elevation of excitement and I see joy as a constant sense of well-being.
I often laugh out loud when I am happy but I don't want to constantly laugh out loud. I might not constantly smile but I do find myself smiling on the inside a lot. Smiling is easy for me but not if I try to force it.

I've noticed a lot of people work really hard to prove to themselves they are happy. Often, they will think that if they are not happy they are sad but it doesn't work like that.
For them, the quest to find happiness all the time actually causes their sadness. They see contentment as a failure to find happiness.

Another thing I've noticed is that some people are not happy but miserable. They do everything in their power to spread misery to others so they can feel better about their own misery. When they see someone that is joyfully content, their goal is to make them miserable. They are jealous of joyful people. Think of all the people you know and consider what I just said. I'm sure at least one fits the bill.

I see this in forum communities all the time. Not just dating forums but the dating forums has more examples. When I was growing up it was called being a "Downer". These people are often locked into a negative mindset.
They don't see the inspirational speaker as a positive. I have heard them say too often, He's just a "Happy Go Lucky" fool. Attend a few seminars and watch the reactions of the audience and you will see what I mean.