～てはじめて— Only After

• 親になってはじめて、親のありがたみが分かった。

  Oya ni natte hajimete, oya no arigatami ga wakatta.

  Only after becoming a parent did I understand my parents' kindness.

  なって + はじめて marks becoming a parent as the trigger for the realization.

• 失ってはじめて、その大切さに気づく。

  Ushinatte hajimete, sono taisetsusa ni kizuku.

  It's only after losing something that you realize its importance.

  失って + はじめて shows realization comes solely after the loss.

• 海外に住んではじめて、日本の便利さを実感した。

  Kaigai ni sunde hajimete, Nihon no benrisa wo jikkan shita.

  Only after living abroad did I truly feel how convenient Japan is.

  住んで + はじめて makes living abroad the precondition for the feeling.

• ・Meaning: the second clause was impossible or unnoticed before the first action.
• ・Common with verbs of realization (分かる, 気づく, 実感する).
• ・はじめて here means 'for the first time / not until', not literally 'begin'.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～てはじめて is tested against.

• に際して — On the Occasion Of
• に先立って — Ahead of the Event
• につけ — At Every Turn
• ～にわたって — Spanning the Whole Range
• ～たび(に) — Every Single Time
• ～あげく(に) — After All That, In the End
• ～折(に) — On the Occasion Of
• ～かと思うと／かと思ったら — No Sooner Than, Just When