carefulness vs careless

carefulness is a noun but careless is not a noun.

Word	Noun	Adjective	Verb	Adverb
carefulness	Yes	No	No	No
careless	No	Yes	No	No

carefulness (noun)	careless (noun)
the quality of being careful and painstaking
the trait of being cautious; being attentive to possible danger

carefulness (adjective)	careless (adjective)
	marked by lack of attention or consideration or forethought or thoroughness; not careful
	effortless and unstudied
	(usually followed by `of') without due thought or consideration