Good—better—best. Some of us may remember learning in grade school very specific rules about when to use ‘better,’ as opposed to ‘best.’ Same with elder or eldest, older or oldest, younger or youngest. For instance, because I have only one sibling, I am “the younger,” never “the youngest,” of my parents’ offspring.
When I began to think about silly expressions recently, I wondered about “put your best foot forward.” Granted, “put your better foot forward” doesn’t have much of a ring to it, but, still . . . it’s quite an odd saying. So are “piece of cake,” meaning easy, and “piece of work,” meaning crazy. There are hundreds of idiomatic expressions that mean something not obvious, but add in less-than-good grammar, and you have to pity the student of our language.