矢先に・
矢先 marks the critical moment just before something begins or just after it has begun or happened, when an unexpected development interrupts or overturns the expected course.
The expected course is interrupted
The first event must create a meaningful expectation: a plan is about to start, recovery has begun, or a new situation has just been established. The second event then arrives at exactly that critical point and changes what was expected. This is why the expression is much more emotionally charged than an ordinary time expression.
Two timing boundaries
The historically central use looks forward to an action that is about to begin. Established modern usage also places the unexpected event immediately after a completed action.
私たちが発表を始めようとした矢先に、会場が停電し、開始できなくなった。
Just as we were about to begin the presentation, the venue lost power, making it impossible to start.
AnalyzeThe power failure prevents the planned action from beginning.
新しい店を開いた矢先に、近くで大規模な工事が始まった。
Just after we opened the new shop, major construction began nearby.
AnalyzeThe shop has already opened; the construction is an unexpected development immediately afterward.
Linking the critical moment to a noun
海外赴任が決まった矢先の病気で、私は計画を見直さざるを得なかった。
Because I became ill just after my overseas posting was decided, I had no choice but to reconsider the plan.
Analyze矢先の links the illness to that critical point in the developing plan.
Critical timing versus a completed endpoint
矢先 highlights an expected course being interrupted at a critical moment and can refer to just before the first action begins. By contrast, たとたん places the second event directly at the completed endpoint of the first action.
外に出たとたん、雨が降り出した。
The moment I stepped outside, it started to rain.
AnalyzeThis neighboring pattern anchors the rain to the completed act of stepping outside; it does not express an interruption before that action begins.
More examples
私は退院した矢先に、また高熱を出した。
Just after leaving the hospital, I developed a high fever again.
Analyze家族で旅行に出かけようとした矢先、息子が熱を出した。
Just as the family was about to leave on a trip, our son developed a fever.
Analyze業績が回復し始めた矢先に、主要な取引先が倒産した。
Just as business performance had begun to recover, a major client went bankrupt.
Analyze私が引っ越しを決めた矢先の転勤命令で、計画は白紙になった。
A transfer order that came just after I decided to move forced the plan to be abandoned.
Analyzeようやく問題が解決した矢先に、別の不具合が見つかった。
Just after the problem was finally resolved, another defect was discovered.
Analyze応募を諦めようとした矢先に、採用の連絡が来た。
Just as I was about to give up on the application, I received notice that I had been accepted.
Analyze担当者が契約書に署名しようとした矢先、条件の誤りに気づいた。
Just as the representative was about to sign the contract, they noticed an error in the terms.
Analyze