The following is an answer and/or comment by inhahe aka ColorStorm (inhahe.com - myriachromat.wordpress.com).
Some people think of success in more worldly terms, such as making a lot of money, being high in social status, meeting career goals, having a wife and family, etc. In those terms you can easily be successful and not happy. I think maybe some people take "success" to its logical extreme though and conclude that true success is being happy, nothing more or less. That's the way I see it, at least. What's the point of having any amount of "success" (by some person's or society's definition) if you're not happy? And if you're happy why do you need anything else? Isn't our goal in life almost by definition to be happy?

Reminds me of the popular story (probably falsely) attributed to John Lennon: "When I was 5 years old, my mother always told me that happiness was the key to life. When I went to school, they asked me what I wanted to be when I grew up. I wrote down �happy�. They told me I didn�t understand the assignment, and I told them they didn�t understand life."