Know Which Side One's Bread Is Buttered On Meaning

Example : 1822, Sir Walter Scott, The Fortunes of Nigel, Chapter I:  â€œPshaw!” answered his mercurial companion; “he knows on which side his bread is buttered, and I warrant you has not lived so long among Englishmen, and by Englishmen, to quarrel with us for bearing an English mind."1909, Jack London, Martin Eden, Chapter XXIX:  They are all stupid when they are not crafty, and very few of them are crafty. The only wise Republicans are the millionnaires and their conscious henchmen. They know which side their bread is buttered on, and they know why."1922, James Joyce, Ulysses, Episode 16:  He knows which side his bread is buttered on though in all probability he never realised what it is to be without regular meals.2003 October 9, Ken Fisher, “Pentium 4 Extremely Expensive Edition, cache boost for everyman”[1], Ars Technica:  On the other hand, the decision to beef up the standard fare without raising prices is a signal that Intel knows which side of the bread is buttered.