Joy is the emotional shape of Truth.
“Truth” is not something that happens in thought. No matter how “true” a thought is, it is still a representation of truth, not Truth Itself. Real Truth is what really is, not what we represent in our minds. Real Truth, then, is always what is actually happening in the present.
The beholding of Truth is openness, and the reflection of that openness in the body is joy. Even if what is happening in the moment is misery, openness to the misery makes a space within which joy can once again sprout. Thinking about miserable things will perpetuate the misery; but openness to the misery dissolves it. So do not make joy the goal; be open. Joy comes by itself.