What is one common thing among TVXQ's Yunho, SHINee's Taemin, and EXO's Kai who are known to be one of the most talented ones among idol groups? Many idol members go through 3~5 years of training before debuting, but even though the hours of practice every idol group member spends may be the same, what is the difference between those who improve and those who don't show progress?

The "10,000-hour rule" states that whatever natural talent one has, in order to become a worldwide professional, 10,000 hours of practice is needed. In SBS special "Hard Working Idols," the secret behind the 10,000-hour rule will be revealed.

How did SHINee's Taemin, who had revealed that he used to be tone deaf when he was younger, overcome this obstacle to be where he is today? The stories of Taemin and his best friend EXO's Kai, of them being each other's teacher and competitor while being trainees together and the real hearts they had towards each other when being trained together will be revealed for the first time through "Hard Working Idols."

This episode will be aired on February 16.

Photo Credit: SBS