矢先に・
You were just about to do something, or had only just done it, and right then something happened that cut across it. Mostly it is a story of bad timing.
about to
Just as we were about to leave on a family trip, our son came down with a fever.
only just
We had only just opened the new shop when major construction work began nearby.
About to
Verb in the volitional form + とした + 矢先（に）
出かけよう → 出かけようとした矢先に. The に is optional. Also ようと思っていた矢先に, "just as I was thinking of".
Only just
Verb in the た-form + 矢先（に）
退院した矢先に, just after leaving the hospital.
Before a noun
… 矢先の + noun
退院した矢先の事故, an accident just after leaving the hospital.
- Before it
- What you were about to do, or what had only just happened: 寝ようとした, 出かけようとした, 退院した, 決まった.
- After it
- What happened right then, mostly something unwelcome: a phone call, an illness, an accident, bad news. Not something you chose to do.
- Where you'll meet it
- News and written accounts, and people telling the story of what went wrong.
In use
Just as we were about to begin our presentation, the power went out in the hall and we couldn't start.
Just as I was thinking it was time I called her, she got in touch with me.
A happy coincidence this time.
I had only just decided to move when I was ordered to transfer, and the plan was scrapped.
With の, what happened is a noun: 転勤命令.
矢先に or ようとしたら?
I was about to go to bed when the phone rang.
Everyday: what happened as you went to do it.
Just as I was about to go to bed, the phone rang.
The same, told as bad timing: then, of all moments.
Close neighbours
たとたん（に）N3
The everyday one. The very moment one thing was done, something else happened, suddenly and not by your choice.
The moment I sat down, the phone rang.
Two things one right after the other, told by someone watching. The second is often the opposite of the first. Not said about what you did yourself.
No sooner had the baby fallen asleep than it woke up again.
The verb twice, plain and then negative: "had barely … when". The second thing begins almost on top of the first.
He had barely sat down when he stood up again.
Check yourself
1Had the person gone out when the visitor came?
出かけようとした
Choose an answer to see why.
2Which ending fits?
風呂に
Choose an answer to see why.
More sentences
Just as business had begun to pick up, a major client went bankrupt.
I had only just left the hospital when I ran a high fever again.
The problem had only just been solved at last when another fault turned up.