Can't intentionally smiling release the same chemicals in your brain that are released when you are happy about something in a sort of backwards effect?
Fake it till you make it?
I definitely think this helps in case of happiness, since a 'deliberate' smile makes folks around you friendlier and happier. That, in turn, enforces the same emotion on to you!
There is a lot of truth to "ignorance is bliss", a healthy dose of ignorance is often times necessary.
What do you really gain by being all knowledgeable (and miserable)? Life is not a videogame that you win at the end by learning more than other people, instead it's a game that we all LOSE when we die, so to my eyes the only thing we should optimize for is to be happy while we live. If knowing more things make you happy, go for it but keep an eye on the potential negative effects on one's mood/happiness that I find inherent in knowledge.
The secret is something else, I think: happiness is a temporary emotion. It is not meant to be a constant long-term state of being. What people really want is contentment, but because the narrative tells them they must be happy all the time they seek that out instead, and through suffering often achieve it for moments at a time before returning to baseline. Then they have to set a new goal for the next hit.
To others to yourself. To everyone.