What is the meaning of [Don’t bark if you can’t bite]

“I made the statement years ago which is often quoted that 80 percent of life is showing up. People used to always say to me that they wanted to write a play, they wanted to write a movie, they wanted to write a novel, and the couple of people that did it were 80 percent of the way to having something happen.”,Woody Allen, Interview for The Collider (2008)