Two atheistic assumptions:
1) Maximal joy does not likely come with maximal belief in truth and minimal belief in falsehood.
2) We have no transcendent duty to maximize our belief in the truth and minimize our belief in falsehood.
Convincing a person that they “ought” to pursue the truth at all costs requires convincing a person that these are false assumptions. But how can you really convince a person of that? One could ask, “How do you know that, when one has discovered the truth, it won’t be terribly depressing?” And one could say, “If Truth is not an ultimate person, then none of us are obliged to it.”
Hence, it must be seen with the eyes of the heart.
“[He] has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.” (2 Corinthians 4:6)
 “Ought” here means both “moral obligation” and “rational means to an end.”