bumbler vs sad sack

bumbler and sad sack both are nouns.

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

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

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

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

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