If you're just saving and not investing, you're setting yourself up to lose money in the long run. That's a lesson Danielle Town, author of "Invested: How Warren Buffett and Charlie Munger Taught Me to Master My Mind, My Emotions, and My Money (with a Little Help from My Dad)," learned the hard way.

When Town, then 34, found herself burnt out as a corporate attorney, she started brainstorming ways to retire faster. "I started to think, 'What else can I do to support myself without being dependent on my salary?'" she tells CNBC Make It.

Her first instinct was to hoard as much cash as she possibly could.

"What I was doing was saving money, which I thought was genius," she says. "And I felt very comfortable with my money, figuratively, under my mattress, just protected, and careful, and safe."

As she writes in her book, "it wouldn't grow much, I knew, but it wouldn't get smaller either."