Tim Ferriss is a very successful guy by just about any conventional standard. Since the release of his massive bestseller The 4-Hour Workweek 13 years ago, Ferriss has amassed a fortune, released four other successful books, started a popular podcast, invested in numerous startups, and generally come to be regarded as one of the smartest voices on personal excellence around. 

But there's one definition of success Ferriss didn't manage to attain: his own.

In a revealing interview with GQ recently, the productivity guru explained that for years after his breakout book he was actually chasing the wrong goals. It's only recently he defined -- and started to achieve -- true success. 

"Successful" but still miserable 

Each book he has written, Ferriss explains to interviewer Clay Skipper, is aimed at maximizing output in a particular area. 

With The 4-Hour Workweek, "the objective was to provide a toolkit for maximizing per-hour output," he says. "4-Hour Body was providing a toolkit for physical optimization and body recomposition. 4-Hour Chef was a toolkit for accelerated learning. Tools of Titans and Tribe of Mentors combine all of those, plus the toolkit of psycho-emotional health."

But despite writing all those books, Ferriss noticed that while he was richer, smarter, and fitter, he wasn't appreciably happier. "I found myself, after checking a lot of those boxes, still suffering," he admits. And he's not alone. "I know centi-millionaires and billionaires who are utterly miserable," he adds. 

With this realization, Ferriss began a years-long journey to quiet his inner demons and learn to live comfortably in his own skin. Fame and fortune are nice, but peace of mind, he realized, is the true definition of success. 

"It doesn't matter how much money you have, doesn't matter how effective or efficient you are. It doesn't matter what types of fancy toys you collect. It doesn't matter how hot your significant other is, if your inner world--your internal monologue or dialogue--is that of anger or despair or frustration or sadness the majority of the time," he explains. 

Without peace of mind, what's the point of a million- or billion-dollar net worth? Without loving yourself, how can you love anyone else? (A truth RuPaul famously understands as well.) Success without self-acceptance isn't success at all

What to check besides your bank account or follower count 

The long interview goes into detail about Ferriss's ongoing quest for internal as opposed to external success, including recommendations for books that upended his thinking and a lot of enthusiasm for psychedelics. Check it out if you think these tools might be useful to you, but one of Ferriss's insights is something just about every ambitious striver needs to hear. 

It's easy to measure conventional success. You look at your bank balance, check your follower count, or show off the flashy car in your driveway. Measuring real, internal success is harder. Nevertheless, Ferriss suggests a clear marker of whether you've made it psychologically that anyone can use as a benchmark for their interior progress.

"How do you feel when you wake up and before bed and how easily do you fall asleep? The time in bed in the morning and at night tells you all you need to know," Ferriss claims. 

Do you wake up anxious or energized? Do you want to get out of bed or hide under the covers? At night, do you drift off peacefully or battle circling worries and nagging regrets? If you want to see if you're successful, Ferriss suggests, all you need to do is ask yourself how you sleep at night. 

"I would find it difficult to call myself successful if I'm experiencing anxiety, fear, regret when I'm in bed in the morning or before I go to bed," he concludes. More of us should probably adopt this definition of success.