I’m still in Happiness in the quote book.  This one sounds surprisingly like a Bible verse or two.

If an Arab in the desert were suddenly to discover a spring in his tent, and so would always be able to have water in abundance, how fortunate he would consider himself; so too,  when a man who… is always turned toward the outside, thinking that his happiness lies outside him, finally turns inward and discovers that the source is within him.
– Soren Kierkegaard