The happiest people work for companies that have some or all of these things nailed.
I've been very fortunate that for most of my professional life, I've worked in careers I absolutely loved — and Upworthy is one of them! One big reason I've frequently been paid to do what I love is that I have indeed felt engaged and challenged on a regular basis. How about you? If not, maybe print this off and leave it somewhere ... say, on a break room table?