This might not be much of a secret to most of you reading this but I believe the secret to true happiness is knowing Jesus. I had a guy at work say "you don't know much of anything do you". His words made me want to lash out at him. I thought for a while and instead of doing a flying knee to his jaw bone, I decided to let it go. The most important thing to know is Jesus Christ and Him crucified. This is what the apostle Paul said in 1 Corinthians 2:2.
"Yet we do speak wisdom among those who are mature; a wisdom, however, not of this age nor of the rulers of this age, who are passing away; but we speak God's wisdom in a mystery, the hidden wisdom which God predestined before the ages to our glory..." (1 Cor.2:6-7) "The secret He reveals has nothing to do with having happy thoughts in order to obtain happy things; it has to do with having the mind of Jesus Christ (v.16).
"Therefore there is now no condemnation for those who are in Christ Jesus".(Romans 8:1) There is a law that made us free (v.2).
The secret is to walk with God, and lean upon His Word. To know lasting happiness, we must get to know Jesus.