Tony Robbins went from working as a janitor to being a multi-millionaire who sells inspiration for a living. And Warren Buffett, one of the most successful investors of all time, is currently worth almost $75 billion.
Both of these legendary businessmen say the best investment they ever made was not a stock or financial asset. It was a class.
When Robbins was 17 and earning $40 a week, he spent $35 for a three-hour seminar with personal development coach Jim Rohn.
The course taught Robbins that the most important work he could do in his life was on himself.
"[Jim Rohn] made me stop focusing on what was outside of my control … and taught me to focus instead on what I could control," Robbins writes in his book "Money: Master the Game." "I could improve myself; I could find a way to serve, a way to do more, a way to become better, a way to add value."
Buffett learned a similar lesson. He was terrified of public speaking when he was young. To force himself to face his fears, at age 20, Buffett signed up for a public speaking course with the Dale Carnegie institute.

After graduating from the course, Buffett went to the University of Omaha and, to fully overcome the phobia, asked to teach a class, recounts Tim Ferriss in his book about the habits and processes of successful people, "Tools of Titans."
Robbins tells Ferriss he has heard Buffett say that "investing in yourself is the most important investment you'll ever make in your life." And Robbins agrees.
"There's no financial investment that'll ever match it, because if you develop more skill more ability, more insight, more capacity, that's what's going to really provide economic freedom. … It's those skill sets that really make that happen."
See also:
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Tony Robbins: Use this 3-step process to achieve anything you want
Tony Robbins: To be truly successful, avoid these 3 mental traps
Tony Robbins shares the 10-minute morning routine that sets him up for success
4 public speaking lessons from the class that changed Warren Buffett's life
