When I look at successful people around me, even if there is one dominating trait, the key seems to be knowing what to pull out when. You can be the smartest person in the world but if you can't communicate it properly, no one will ever know or care.
Everyone thinks that beautiful people have it easy, but truly, if all you have going is looks you're not going to go far. You have to know when to flirt, how to flirt, how to tell which people won't respond. If one is beautiful but not too bright, it is very easy to be taken advantage of.
Athletic ability...will get you success for a short time, if you are extremely lucky and in the top 0.5%. But if you don't have any intelligence to go with it, the million-dollar salary is wasted and you end up with a heart attack at 50 because you haven't changed your training routine since high school.
There is so much more to intelligence than simply being smart. I can memorize all the figures you want, calculate quick mathematical equations in my head, make logical connections that take some time to explain to most. But I also have a need to be right all the time, inevitably get interested in stuff that no one around me cares about, and can be difficult to be around.
That doesn't mean my knowledge is worthless, it just means that there is more than one personality trait necessary for happiness. Happy people I know come in all different flavors - some are smart, some are compassionate, some are funny, some know just how to dress, some know how to make anyone feel good. Are any of those traits worthless?