In a letter published in the British newspaper the Daily Mail Cowell subjects himself to the same harsh criticisms he's showered upon hundreds of "Idol" contestants.
"Look at you. You look like a complete idiot... You are overconfident, far too cocky and dressed from head to toe in expensive designer gear," Cowell writes to a younger version of himself. "Stop it, Simon. This is embarrassing. You are making me cringe."
The self-addressed letter, a retrospective that alternately lashes out at and encourages his younger self, chronicles Cowell's meteoric, yet short-lived initial success in the music industry, the sobering big crash that followed and his eventual return and unprecedented success.
The revealing reflections, entitled "A Letter to My Shallow, Reckless, Cocky Younger Self," come as "American Idol" judge's 50th birthday looms on Oct. 7.
Cowell is especially critical of the 1980s version of himself, the one that drove a Porsche, wore expensive clothes and went to elite restaurants and nightclubs, all the while unable to appreciate it all and much less able to afford it, Cowell writes.
"For two or three years you have earned nothing of substance but you have racked up debts of nearly half a million quid. On what? On junk," Cowell writes. "Suddenly it all grinds to a halt. It's over!"
Under a mountain of debt, Cowell moved back in with his parents. Oddly, Cowell said he felt his personal crash was a "huge relief."
"Yet the funny thing is, what you don't know, Simon, is that you will never again feel so carefree in your entire life," he writes.
Simon Cowell Looks Forward to Birthday Party
Cowell clawed his way out of debt month by month and remembered the day he cleared his debts as one of the happiest of his life. From this, Cowell draws the biggest life lesson he wishes he could have known earlier: "Only buy what you can afford."
"Simple as that," he writes. "Carrying a debt is a much bigger burden than having nothing."
His struggle to get back to the top was slow and painful.
"You feel that everyone is laughing at you behind your back," he writes. "Do you want to know something, Simon? That's because they are... You are distinctly Not Cool."
Cowell said his "instincts" kept him on the road to success, and now, as "American Idol" enters its ninth season, Cowell is reportedly pulling in at least $36 million.
In the letter Cowell says he has "no regrets" about never getting married and says that "family life would be a problem now." Celebrity, he writes, was never part of the plan.
"For you never imagined, not in your wildest dreams, that you would become well known all over the world. Your job, Simon, was to make celebrities, not become one yourself, dear boy," he writes.
In the letter, Cowell defends himself from the idea he is a "Machiavellian character, forever plotting and scheming" and shows that he is "not a stranger to failure."
Music Business Has Changed
Cowell sees a difference in not only the way music is marketed now -- increasingly by television through shows like "American Idol," a trend he faintly foresaw decades ago -- but also in the way he treats himself.
"What have you learned? Not to drink Galliano, that's for sure. Today, on the eve of your 50th birthday, you are much more likely to drink two litres of water a day rather than a gallon of champagne," he writes.
More than anything, Cowell believes himself a "realist," according to the letter, and has no delusions that his life has been harder than many.
"OK, it is true that no one is ever going to publish a book called "Simon Cowell: My Struggle," he writes. "Your journey has been a breeze compared to the very real difficulties many people face in life and you have met some great people who have helped you."
Looking for his big 50th birthday party, he still remembers the celebrity-filled parties he saw as a boy when his parents lived next door to a film studio boss.
"And what you remember, most vividly, is that you wanted to be at that party," he writes. "You wanted to join in. Well, this time the party is all yours. It is going to be a great night. So happy birthday!"