When Carla Harris's high school guidance counselor told her that she shouldn't waste her time applying to three Ivy League schools, she did it anyway.
It was a good thing she didn't listen. Harris got into all three schools and a few years later graduated magna cum laude from Harvard University.
Similarly, when her peers told her she should stay away from Morgan Stanley's mergers and acquisitions division because it was too demanding, she ignored their advice and went for it.
Today, Harris is a vice chairman at Morgan Stanley and one of Wall Street's most influential women.
When CNBC asked what advice she'd give to her 20-year-old self, she said confidence is key to getting ahead in life.
"Own your power," Harris said, following a panel discussion at an event hosted by the women's leadership platform MAKERS during Advertising Week. "In your 20s, you start to doubt what it is you can do. You doubt why you're in the room. But you're in the room."
The executive said that if you have been given an opportunity, seize it.
"If you got invited to the room, and certainly if you got invited to the table, you are all that," she said. "And you should own that."
Ultimately, she said, your success comes down to believing in yourself.
"Don't be distracted by anything anybody else tells you," Harris said. "Be focused on the truth that you got invited into the room, which means you're really good."