After graduating from the University of Toronto in 1984, and long before he became a celebrity investor through "Shark Tank," Herjavec took the first job he could find as the guy calling people to pay their bills.

"If you're thinking that being a bad-debt collector was not the best way to launch a business career, you're wrong," Herjavec writes in his book "You Don't Have to Be a Shark." "I learned a lot from the job, and some lessons — valuable lessons — stay with me today."

Among those lessons, he says he learned that great salespeople focus energy only on serious prospects, and that empathy is often more effective than aggression when it comes to making a sale.