fumbler vs sad sack

fumbler and sad sack both are nouns.

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

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

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

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

fumbler (noun)	sad sack (noun)
someone who makes mistakes because of incompetence	someone who makes mistakes because of incompetence