firm and stable without any hesitation or change; used to describe a person's position, will, or resolve as being resolute and unflinching

Describes someone who is stupid, ignorant, and too stubborn to change or improve; literally refers to the lowest class of the foolish who never change

(idiom) well established and irrefutable; absolutely reliable and impossible to change

extremely fast, as if the sun has not even had time to move its shadow; used to describe something happening very quickly or on the spur of the moment