A Wall Street performance coach who's consulted on Showtime's 'Billions' too many people have the same misconception about success

For some of Denise Shull's clients, being in a slump might mean losing millions of dollars of other people's money.

Shull is the founder of the ReThink Group, a performance coaching group that specializes in clients on Wall Street. She's also one of the inspirations for Maggie Rhoades, the in-house psychiatrist at the fictional hedge fund at the center of Showtime's hit show "Billions."

Shull studied the neuropsychology of unconscious thought at the University of Chicago and spent 15 years as an equities trader. They are two worlds she combined when she started ReThink in 2002, putting her own spin on the niche market of Wall Street performance coaching, a path paved by the late psychiatrist Ari Kiev, who was employed by Steve Cohen's hedge fund SAC Capital.

Perhaps the most defining characteristic of Shull's approach is that nearly all of us, regardless of what industry we are in, have a misconception about how the mind works and thus how we can recover from failure: We think we can will ourselves to success.

"The conventional wisdom on feelings and emotions is just wrong," she told Business Insider.

Shull thinks many people have assumptions based on an outdated theory of the "triune brain," which basically says emotions, thoughts, and basic functions are handled separately within the brain; the reality, she says, is that all three of these roles are related in brain mechanics.

Too many people, she said, think that "if we have a plan and that we're disciplined then we'll be able to do the things that we want. ... It doesn't work like that."

It's why Shull has clients in the first place, she explained. The clients know that they are underperforming and they see their mistakes. But no pep talk from a manager or colleague and no Stoic denial of feelings can get them back to their peak.

Instead, she recommends her clients - and anyone else struggling through a slump - identify and name the feelings they are attaching to the weaknesses causing them to fail, and dive right in. By embracing these feelings, her clients can come to understand them, strip them of power, and then replace them with desired emotions. The thoughts follow the feelings, she insists, counter to what people often think.

"Sometimes I feel like I'm just going to gag, if I have to read 'mental toughness' one more time," she said. "Like ugh, just being tough doesn't get you the result you want. It fails you at the worst possible moment. ... And then all those feelings come crashing in and cause you to be self destructive or not perform up to your potential."