sad sack vs stumbler

sad sack and stumbler both are nouns.

Word	Noun	Adjective	Verb	Adverb
sad sack	Yes	No	No	No
stumbler	Yes	No	No	No

As nouns, sad sack and stumbler are synonyms defined as:

sad sack and stumbler: someone who makes mistakes because of incompetence

Other synonyms of sad sack include blunderer, botcher, bumbler, bungler, butcher, fuckup, fumbler.

sad sack (noun)	stumbler (noun)
someone who makes mistakes because of incompetence	a walker or runner who trips and almost falls
	someone who makes mistakes because of incompetence