impetuous

acting rashly and quickly

Roots

-ous / -ious: full of or marked by a quality
in- / im- (in/into): in, into, within, or on
pet / petit: seek, aim at, rush toward, or attack

Other words with the pet / petit root

appetite: desire for food or strong wanting
impetus: driving force or stimulus
petition: a formal request
petulant: childishly sulky or rude

Impetuous action rushes toward the thing before judgment has time to stand up.

His impetuous reply created a problem that one calm minute would have prevented.

Impetuous belongs with motion and attack more than with calm decision. The old force is a rushing-toward. Picture a reply sent too fast, a purchase made too fast, a door opened before anyone checks what is behind it.