Always and forever we are told to seek the truth in all matters. But there is rarely a reason given for this. If the reason for seeking the truth is to live in harmony with reality, to navigate reality, fine. But it may be argued that what people really want is happiness, even if that means floating on a carpet above reality. What would be the value of living in harmony with reality if doing so made one miserable? It would have to be asserted that living in harmony with reality is more important than happiness. But one could go a step further: Authenticity--the need to be true to oneself--is a deeper layer of living in harmony with reality. In this case, the true self can be found only in the true reality. I not only navigate reality, I navigate myself to arrive at reality.
Let us assume that this navigation of true reality via the true self is superior to happiness. "Happiness" is rooted in the root "hap," as in "happenstance." So the basic premise of happiness is that it is the result of chance. Joy, on the other hand, is attained or given as a boon. Joy has a deeper level of satisfaction and stability than happiness. There is a recognition in joy of having either arrived at a desired outcome (and usually a deserved outcome) or of being loved. This recognition is absent in happiness.
But does joy derive from truth? I will say there is a type of joy which can only derive from having arrived at the truth of a matter. For example, if I pursue a relationship, and I discover that the other person loves me--if that is the truth of the matter, I may, and probably will, feel great joy. This is my treasure hidden in a field, which I have bought with my life. The truth of this love has met a great need. The recognition of this validation is redemptive, and redemption is miles beyond happiness. It lies in the realization of a hope which can only be incorporated into my life by an objective need being met--objective, because it makes me objectively a better person, more useful to myself and to others. But more than that, it means I matter deeply to someone else.
Here is a problem we all have. It is a good problem, let's assume. If I hold a belief system, say Christianity, and I discover that Jesus is not the Messiah, I will naturally be troubled. I will immediately try to reverse this realization by buttressing my faith with some arguments that might reinforce my old belief that Jesus is the Messiah. But why would this trouble me? Can't I simply choose what I believe? I cannot. As a human being I am automatically inclined to believe the truth. This is why so many religious people have a hard time retaining their faith. But this is an absolutely amazing faculty! We are all, or almost all as far as I know, troubled when we face evidence that contradicts what we believe. This means that we all, or almost all, intrinsically care deeply about the truth. But why? What sort of evolutionary advantage does believing the truth hold?
In the case of navigating a hunter-gatherer life, believing something false about the world could quickly mean death. We have carried this concern for truthfulness into everything. It even covers metaphysics. As we grow in our knowledge we grow in our concern. In fact, knowledge without concern is useless. We can only know in proportion to how much concern we possess.
In the case of we humans as hunter-gatherers, we have all made the mistake of living. There is, in fact, a lion in the bush very close to us. To the theist the lion is God. To the atheist the lion is nothingness. We have all made the mistake too late of neglecting to acknowledge that we will return to whatever we came from. The only difference between metaphysics and bush hunting is that we can be eaten alive and refuse to acknowledge it.