know what/which side of the bread is buttered (on), to

know what/which side of the bread is buttered (on), to

To know where one’s best interests lie. This metaphor appeared in John Heywood’s Proverbs of 1546 (“I know on which syde my bread is buttered”), and was used so often over the centuries that it was a cliché by about 1800.
See also: bread, butter, know, of, side, what
The Dictionary of Clichés by Christine Ammer
See also:
  • which way the wind blows, (to know)
  • eat one's cake and have it, too, to
  • quick as a wink/bunny
  • (one's) jollies
  • can't see the forest/wood(s) for the trees
  • (one's) John Henry
  • an all-out effort
  • bacon
  • a good voice to beg bacon
  • a change of scenery