Keep One's Mouth Shut Meaning

Example : 1906, Upton Sinclair, The Jungle, Chapter 25  He thought that he could get him a regular salary if he would come to Packingtown and do as he was told, and keep his mouth shut.2004, Alan Cowell, "Charles Joins Fray Over Himself," New York Times, 23 Nov. (retrieved 25 Oct. 2008):  Charles has failed to follow the example of his mother, the queen, who has heroically kept her mouth shut for more than 50 years.