stumbler vs sad sack

stumbler and sad sack both are nouns.

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

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

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

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

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