With the head leading the way before the rest of the body; also means to do something without careful thought or planning.
Compound of 'head' + 'first,' suggesting the head goes first in order of direction. Has been used since at least the 1600s.
Diving headfirst into water was considered so natural that Victorian parents actually worried about it—they thought rushing into things 'headfirst' was morally dangerous, reflecting how the phrase became synonymous with recklessness.
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