An early retiree used a lesson from 'The Millionaire Next Door' to quit his job at 35 and travel the US - and he'd recommend it to anyone

• Steve Adcock told Insider the book "The Millionaire Next Door" helped him and his wife save $900,000 to retire early and travel full-time at age 35.
• He said it helped him understand that real millionaires live below their means, tucking away more money rather than spending it.
• It's the one book Adcock recommends to every aspiring early retiree.

At age 35, Steve Adcock was ready for a new kind of American Dream.

In 2015, he quit his job in information technology; sold all of his possessions, including two homes; and bought a 200-square-foot Airstream trailer to travel the US full-time with his wife. They had saved $900,000 between long-term investment accounts and short-term savings and checking accounts. By 2018, they were self-made millionaires and full-time travelers running a YouTube channel chronicling their adventures.

They've since moved into a solar-powered home off-the-grid in Arizona. In March and April during the Covid-19 market crash, they lived off a $100,000 emergency fund they saved before retiring that's separate from their spending money and long-term investments. Adcock previously told Insider the fund helped them maintain their standard of living without selling a share of stock.

But the couple may not have been so well prepared for the ups and downs of financial independence if Adcock hadn't read "The Millionaire Next Door" by Thomas Stanley and William D. Danko. He told Insider it's the one personal finance book that had a big impact on him - and the one book he'd recommend to everyone who wants to achieve early retirement.

Living below your means is key to achieving financial independence

"The Millionaire Next Door" analyzes how everyday millionaires quietly make, keep, and grow their money as a way to build a safety net or comfortable retirement. The authors found that many people who built their own wealth and became financially independent have several habits in common, like frugality.

"It helped me to understand how real millionaires live," Adcock said. "Most don't drive around in BMWs, live in the big house on the hill, or shop at ritzy outlet shops."

He continued: "Instead, true millionaires (that is, people who have millions, not just make a high income but spend the majority of it) drive normal cars (like Jeeps and Toyotas), shop at grocery stores just like you and me, and dress in regular clothing."

Rather than spending their fortunes on a large mortgage, multiple expensive cars, and other status items, these millionaires invested their cash. They avoided lifestyle creep, when one increases their standard of living to match a rise in discretionary income, and lived below their means. For them, earning more meant saving more, not spending more.

Adcock said that learning this made him not miss the "nicer" things in life, because they wouldn't help him achieve financial independence and early retirement. As he put it, "I learned the acquisition of that stuff could very well prevent - or at least delay - me getting there."