How do you live a fulfilled, happy life as a common person?

I heard these all the time: "You always think grass is greener on the other side", "people always want what they don't have", etc.

For those who live every day, not being jealous/crave what others have, and being grateful for your life, waking up each day excited, what are your secrets? Is it hobbies, financial independence, SO, or other? How does one reach that state of self-satisfaction?

Perhaps it's my quarterlife crisis, but I have been thinking about this a lot...