Self-made millionaire Barbara Corcoran was called "the 'dumb kid' in school," she told CNBC Make It in November, as she struggled with undiagnosed dyslexia.

"I was labeled the 'dumb kid' that couldn't read or write, coming all through to when I was graduating in high school," Corcoran told CNBC Make It. As a result, she was a straight-D student throughout her childhood.

But Corcoran didn't allow this to stop her from achieving success. Now, she even says "dyslexia made me a millionaire," as she wrote on LinkedIn on Monday.

"I spent 6 hours a day daydreaming in class, and by 3rd grade I just gave up," she wrote on LinkedIn. "My mom's response was, 'Don't worry about it. You have a wonderful imagination; you'll learn to fill in the blanks.' That was powerful for me, and I've leaned on that my whole life."

When imagination turns into reality

Corcoran used her imagination to help her achieve success in her career, she wrote.

"At 23, I dreamed I would become the 'Queen of New York Real Estate.' Years later I was running the biggest shop in town, and I couldn't have gotten there without those years of daydreaming."

After working 22 different jobs, Corcoran began her career in real estate as a receptionist for the Giffuni Brothers' firm. She worked there until Ray Simone, her boyfriend at the time, loaned her $1,000 to start her own real estate firm. In 1973, Corcoran began selling apartments on the Upper East Side of Manhattan with seven agents working for her firm.

Ultimately, Corcoran turned the $1,000 loan into a real-estate empire – in 2001, she sold her firm for $66 million.

She said the bullying from her teachers and classmates drove her to work harder and learn the skills she needed to succeed.

"My teachers and classmates constantly calling me dumb only made me more determined to prove myself," she wrote on LinkedIn. "I worked harder than anyone to overcome my 'weakness,' and it's a large part of my success."

Growing from self-doubt

The name-calling created self-doubt for Corcoran. But like her struggles in school, she says she turned that setback into a strength.

"Self-doubt makes you over-prepare so you can't caught with your pants down," she said on LinkedIn. 

According to Corcoran, self-doubt is "a human element that keeps you on the straight and narrow," as she said on a recent episode of her podcast "888-Barbara." 

"The curse of being competent is self-doubt, because competence rides on your own self-doubt," Corcoran said on her podcast. "Everyone I know who has been enormously successful" struggles with self-doubt, she said.

Corcoran also says dyslexia gave her "great empathy," which made her a better leader.

"When you're labeled the 'dumb kid' by your classmates, you develop empathy & kindness towards others because you need it shown to you," she wrote on LinkedIn. "People trust a kind person, and if they trust you, they'll follow you."

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Disclosure: CNBC owns the exclusive off-network cable rights to ABC's "Shark Tank."