on the spur of the moment 즉흥적으로

spur (비유적으로) 박차, 자극제

This is not a spur-of-the-moment decision.

: impulse decision

+

순간적인 충동으로
* cf. on impulse, on the spur of the moment (순간적으로 자극받아) ; whimsically
* cf. at whim (순간적 기분에 따라서)

https://open-pro.dict.naver.com/_ivp/#/pfentry/12fe9d3dd361445e9e89cbea6ef1c38a