I'm not familiar with Mischel's work, though he's admirably produced a lot of it, no doubt reading some of it would teach me things worth knowing. I'm not assuming the article is truly representative of the breadth of such a prolific mind. My ideas on the subject reflect what I've seen and learned so far.
To say we are driven by limbic system emotion in one way and goal-driven prefrontal cortex (PFC) opposing it would be minimizing the magnificent complexity of our construction. Thing is, control of our own behavior is limited and the nature of such control hardly understood by neuroscience, leaving us in no position to confidently prescribe methods of self-control in general.
It should not be surprising that kids performing better on a test that measures exactly what is successful in school and the corporate world will be more successful than kids scoring poorly. Academic achievement requires a talent for anti-hedonism, and those not as gifted in this trait will likely not do as well.
OTOH the persistent stubbornness ("grit") required for some kinds of success isn't synonymous with pleasure denial as seems to be implied. Determined persistence has a strong emotional component, individuals with such traits take pleasure in their accomplishments even if others don't understand it at all. They also react strongly to attempts to deflect them from their path.
Emotional salience is intrinsic to strongly bound goals, one must have the desire, the drive in order to sustain the effort to achieve. The emotion is not suppressed but harnessed in service of the mission. To the goal-seeker, foregoing other pleasures "normal" people covet is not a sacrifice, it is simply unimportant and not missed.
In this paradigm, imagine the kid who's more eager to finish building the tower of blocks than interested in the taste of candy.
History shows us many people built like that: Paul Erlich (chemotherapy), Thomas Edison, Harold Edgerton, among so many others.
The saying "knowledge is power" applies, fully knowing what we feel and having the "grit" to feel it, connected to logical problem-solving is a very potent tool.
Maybe that's what the article about Mr. Mischel was really trying to say.