"Here's what I mean," says Welch. "I've always been fascinated by Hollywood, and specifically, what makes some people stars and not others," says Welch. "After all, untold thousands of hopefuls flood to L.A. every year and only a handful see their name in lights. Surely talent matters — but it's not everything."

Bestselling management author and CNBC contributor Suzy Welch tells CNBC Make It that there's a single thing that separates successful people from everyone else, and it can be explained in just six words.

There are endless books, podcasts, articles and films devoted to the study of success — why do some people achieve it while others flounder?

Welch says that a few years ago she asked her daughter Sophia, who works in casting in Hollywood, what makes some people more successful than others. Without hesitation, Sophia told her that the people who make it are "the ones who come to Hollywood believing that not making it isn't even a possibility. No matter how many times they fall down, they get up again and keep going."

"Talk about an 'oh yeah' moment," says Welch. "Sophia's observation described virtually every successful business person I've ever met, studied, written or read about. None of them had a plan B."

It makes sense that most people with a plan B don't achieve the same level of success as someone without one, says Welch, because "when you have a safe place to run to when things get tough, you can, and often do." By contrast, "people who see their end goal as the only alternative stay on the track that gets them there — bumps, bruises, setbacks and delays be damned."

"Here's my question for those of you with a big dream," she says. "Do you also have a fallback strategy?" If you do, Welch says she doesn't blame you for planning ahead.

"Just know," she warns, "your plan B, as sensible as it seems, may be exactly what undercuts the amazing plan A for your life."

Suzy Welch is the co-founder of the Jack Welch Management Institute and a noted business journalist, TV commentator and public speaker. Think you need Suzy to fix your career? Email her at gettowork@cnbc.com.

Video by Beatriz Bajuelos Castillo

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