This is tone-deaf pop psychology at its worst. Anyone who truly understands "happiness" doesn't strive for happiness as an end unto itself. Happiness is an emotion, a fleeting feeling; good luck defining "happiness" as a concrete thing that ten people can agree on.

Religions and allied philosophies do not attempt to offer unadulterated "happiness" to practitioners. Instead, you can strive toward "joy", and "peace", and "contentment", and things like that. And yes, it is definitely possible for a human being to achieve contentment and peace in this life, the kind which brings an enduring and impreturbable joy. I have known people like this. There really is truth behind the saying "Whoever believes in Me shall never thirst."