The quality or state of being careful; the practice of paying attention to avoid mistakes, danger, or harm.
From careful (Old English care, sorrow/anxiety, + -ful) plus -ness (state or quality noun suffix). The English word evolved from the idea of caring as paying anxious attention to details.
Carefulness evolved from an old meaning of 'care' that meant worry or anxiety—so being careful literally means approaching something with the same worry-driven attention you'd give a sick friend.
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