His conclusion is that the most effective way to increase long-term happiness is not to do things because they make you happy, or to do things that will gain the things that will make you happy.
The most effective way to increase long-term happiness is to engage in activities that make you enthusiastic about what you're going to do.
So meditation doesn't make Buddist monks the happiest people on the planet. Buddist monks are the happiest people on the planet because they know that tomorrow, they get to meditate again.
Homework: Fill in the blank with the word that would make you the most enthusiastic:
"Tomorrow, I get to _____ again!"
Then do that today.