Comfort Zone

They say you have to leave your comfort zone to be the best version of yourself.
But how come? How come you'd be the best version of yourself if you're not comfort at all?
What is more important than comfort?
If you're not comfort enough for what are you doing then will you give your best? Would you do it wholeheartedly? Is it worth at all? Is it easy?
I don't really think so.
Because,
It's all about comfort, someone said.