“When I was 20, I was like, if only I could have the Ferrari. If only I could have the mansion,” Morgan Housel told Fortune. “Looking back, I think the reason I wanted it so badly is because I had nothing else to offer the world.”

Today, younger Americans face greater challenges. Whether it’s grappling with high costs of living, unemployment or stagnant wages, they’re discovering those adult milestones their parents had are increasingly out of reach. While some may deem their irresponsible financial habits as “doom spending,” Housel thinks it’s all just part of growing up, for one key reason: They haven’t had any real purpose yet. 

Housel is known for his bestseller The Psychology of Money, which dissects how people’s previous beliefs, behaviors, and emotions impact finances. Now, he’s unveiling the psychology behind spending in his new book, The Art of Spending Money. 

Housel’s “purpose” for example, was gaining respect through becoming a dad and an admirable husband. When those factors became his compass for success, the desire for that amazing fleet of cars diminished. 

“My aspiration for material stuff is the inverse of what else I have to offer the world,” he added. 

On the flip side, Gen Z’s frustrations revolve around not having the money to achieve milestones like settling down and starting a family. Instead, many are finding comfort in smaller luxuries, like pampering their pets and spending their Sundays waiting in line for a Starbucks Bearista cup.

Housel says spending is not about getting things down to a science; rather, it’s an art that shouldn’t have a “one size fits all” approach. How you’re spending it also makes all the difference: if a majority of your expenditures are material items, you haven’t yet learned the most important life lessons. 

One billionaire says she stopped spending when she no longer had to prove herself

The practice of needless spending doesn’t only hold true for typical debt-burdened Gen Z, it’s also common among millionaires. 

For example, Scale AI’s 30-year-old billionaire founder Lucy Guo still shops at Shein and pulls up to work in a Honda Civic, but before she made it to the top, she says she was guilty of spending needlessly. And according to Guo, if you see millionaires wasting money on designer clothes or a nice car, it’s usually an indicator they’re overcompensating for something else. 

“Who you see typically wasting money on designer clothes, a nice car, et cetera, they’re technically in the millionaire range,” Guo previously told Fortune. “All their friends are multimillionaires or billionaires, and they feel a little bit insecure, so they feel the need to be flashy to show other people, ‘Look, I’m successful.’

Guo isn’t the only billionaire to choose a frugal life. Others, like Warren Buffett, try to lead very normal lives, despite their huge net worths.