When Sam Dogen retired in 2012 at the age of 34 with a $3 million net worth, he made waves as one of the pioneers of the FIRE—financial independence, retire early—movement. Ten years later, he's making waves again—for saying it's time to go back to work.

Dogen, now 45, has written the popular personal finance blog Financial Samurai since 2009. Through it, readers have followed his and his family's journey, from saving for early retirement to leaving the financial industry to writing a book and more.

There are multiple reasons one of the most popular members of the online early retirement crowd is now joining the ranks of the unretired. For one, his investment portfolio, like everyone else's, took a beating last year. Two, he also misses the camaraderie of a workplace. Early retirement is great, but it can also be lonely, he says. There are only so many pickleball games you can play in the middle of the day.

Perhaps the most pressing, though, is because he just can't make the math work on paying for his young children's college education with his current financial situation. When Dogen retired, he and his wife weren't sure they would even have kids. Now they have two, and are raising them in San Francisco. It's expensive, even when you're earning hundreds of thousands of dollars in passive income.

"Life is full of ups and downs and unknowns. You're trying to predict the future, you don't know what’s going to happen," Dogen, who has grown his passive income from $80,000 to around $200,000 a year, tells Fortune.

And you could also argue that Dogen never really retired. Though he left the corporate workforce and lived mostly off of passive income, he also consulted start-ups, produced his blog, and wrote one traditional book and an e-book over the past 10 years. He just did it from the comfort of his home, something that itself is becoming more and more common as some COVID-19 remote work policies remain.