The research I've seen says that having a better sense of reality is correlated with depression. Having a small reality distortion field that allows you spin things in a positive light is a key part of being satisfied with your life.[t]he happiest, most successful children have parents who do not do for them what they are capable of doing, or almost capable of doing . . .The central task of growing up is to develop a sense of self that is autonomous, confident and generally in accord with reality.
Likewise I don't understand how the author sees no trade-off between being happy and successful. There could, of course, be a positive correlation, and the research on flow suggests that people who succeed doing things they like are happy and likewise it makes sense that people who enjoy what they do will be more motivated. So maybe happiness and success should be correlated.
But mostly you would expect a tradeoff. The way people become exceptional--remember we are talking about "most successful"--is by doing a ton of directed practice. And directed practice is hard work, exhausting, and it sucks. Working 80+ hours a week sucks, even when you generally like your work, when it inevitably cannibalizes your social or family life.
I know from experience that most of the most successful kids, a few years down the road when they are at MIT and Harvard, are not particularly happy.