When Barbara Corcoran set off on her own after college, moving from New Jersey to New York City to try her hand at selling real estate, she lived off money she didn't have.
Between bouncing checks and charging purchases she knew she wouldn't be able to pay within the month, she was a terrible spender.
"By my late 20s, I realized I couldn't afford the things I really desired," Corcoran told Business Insider at a recent event for personal finance resource Zebit.
"And by my early 30s, I realized I had to work like crazy to get what I wanted rather than spending it before I had it."
Only then was she able to become a Manhattan real estate power player, as the head of the Corcoran Group.
The advice she wished someone had told her in her 20s, she said: Spend even a single week only using cash, charging nothing to a credit card.
"When you put it on a credit card, somehow in that moment it seems like great value, but when you're putting cash out--you have limited cash, what you've earned that week--you're surprised at how quickly you realize how much money you're truly wasting," she explained.
There's plenty of research that suggests the average person spends more when purchasing something with credit rather than cash, including a study from Dun & Bradstreet that found people spend 12 percent to 18 percent more on credit.
Business Insider reporter Kathleen Elkins tried the cash-only experiment in 2015, writing about it after two weeks and ultimately stretching it to a full six months. She found that she was able to be more conscious of her budget than ever before, because there was a more tangible feeling as she handed over her cash or saw it deducted from her checking account.
The point of going cash-only is to build the muscle memory required to spend only what you can pay off at the end of the month, even if you're using credit cards for their flexibility and benefits.
"And that's the lesson that I wish somebody had brought to me earlier," Corcoran said.