～がきっかけで ・ をきっかけに

About

The noun「きっかけ」 ("chance; start; motive; impetus") is used to describe the initial reason for a given action. This reason should generally be the direct cause; the precise impetus! Fancy.

きっかけ mainly attaches to nouns, but we can skirt around this somewhat by using nominalized verbs (either の or こと is fine). Certain verbs may attach directly to きっかけ in their present or past casual forms, but these are limited and fairly small in number.

～きっかけ may be used in various contexts, from spoken polite to spoken casual, and even some formal or written contexts. That being said, it's worth noting that 契機けいき and 機きに are more preferable in very formal/written scenarios.

E.g. 友達ともだちの紹介しょうかいがきっかけで、マイクと付つき合あうことになった。 "It was due to a friend introducing us that Mike and I started dating."

E.g. 入院にゅういんがきっかけとなって、タバコをやめました。 "I quit smoking because of my hospitalization."

E.g. 失恋しつれんしたのをきっかけにジムに通かよい始はじめた。 "I started going to the gym after having my heart broken."

Summary

• 

  きっかけ is used to describe the initial reason for a given action

• 

  きっかけ can attach to nouns, as well as nominalized verbs, and certain verbs in their casual forms

• 

  ～きっかけ may be used in various contexts, from spoken polite to spoken casual, and even some formal or written contexts