In He: Understanding Masculine Psychology by Robert A. Johnson, we read:
The word “enthusiasm” is a beautiful word. In Greek it means “to be filled with God.” […]
The implication of this number symbolism may also relate to the Christian doctrine of the Trinity. This is a thorny subject and I don’t want to go very far with it, but it would seem that the Trinitarian view of man’s nature, or the Godhead, is incomplete. The threeness of God requires the inclusion of the fourth to achieve completeness and stability. Anytime one has a Trinitarian system going there will be an adversary somewhere, for something will have been left out. What has been rejected will reappear as the devil, for whenever something of the spirit that belongs to wholeness is excluded it turns against us. Jung has made quite a bit of this and often suggests that what has been excluded from the Christian Trinity is the dark, feminine element in life. So it comes back to plague us as a kind of cthonic evil.[…]
Alexis de Toqueville, a Frenchman who came to America more than a century ago, made some astute observations about the American temperament, atmosphere, and idiom. He said that we have a misleading idea in our Constitution, the pursuit of happiness. One can’t pursue happiness; it won’t work.
A formulation for these days could go something like this: “If you will serve your reality, you will be flooded with happiness. But if you merely search for happiness, you will dispel the very happiness for which you are looking.”