Justin Guarini, the runner-up of the inaugural season of "American Idol," has spoken about the challenging period following his initial rise to fame, describing it as a "dark spiral" that ultimately became a "greatest blessing."

In his book, "Center Stage Confidence: How to Own Your Story and Command Any Room," Guarini recounts the moment in 2003 when he learned he had been dropped by his record label, RCA. He described the experience as his "entire world came crumbling down around my ears." The illusion of fame and fortune vanished, replaced by a profound sense of loss and what he called "the veil of my arrogance, my assumptions, and my entitlement."

Guarini recalled spending months in isolation, feeling unable to face himself or the world. He described losing weight and withdrawing, a change that concerned those close to him. "I was living the ghost of the life I had always dreamed of and burning money and time in equal and absurd measure," he wrote.

His debut album, released in 2003, had a modest debut, and the movie he starred in with Kelly Clarkson, "From Justin to Kelly," was a critical and commercial failure. Guarini faced criticism for his performance and appearance, which compounded his struggles.

However, Guarini eventually began to shift his perspective. He realized that people were still celebrating him and that there was still value in his life beyond metrics like votes or followers. This realization led him back to his passion for performing on stage, regardless of the venue.

"For me, that came in the form of just going out and getting on the stage and singing for people. And I would do it at everything from gala events to state fairs to wherever," he told Fox News Digital.

These performances opened new doors, leading to a Broadway debut in "Women on the Verge of a Nervous Breakdown" in 2010. He went on to perform in other Broadway productions, including "American Idiot" and "Wicked." He also gained recognition for his flamboyant character, Lil' Sweet, in Diet Dr Pepper advertising.

Guarini now views his past struggles as crucial for his personal and professional growth. He stated that embracing failure and continuing to move forward through discomfort allowed him to develop in ways he might not have if his initial fame had lasted. "And so, for me, it has been almost 25 years now of some awesome ups and downs, and every single time I go up and down and up and down, it's just a consistency again of staying in the game," he said.

He believes that in any industry, staying persistent and maintaining kindness are key to enduring success. "This life in this world is cyclical and if you stay in the game, and you do good work, and you're kind to people, the opportunity always comes back around to you, and you'll be more prepared to take advantage of it when it does," Guarini added.