What does happiness look like? What does it sound like? What does it taste like? What does it feel like? What does it smell like?
If writing, be as descriptive of what you think happiness is as possible. Try to make the person experience happiness from your perspective.
Attempt to describe a color to someone who has been blind their entire life.
What does true happiness look like to you or your character? Truly take some time to allow to the reader to feel what you feel.