矢先

1. Origins, structure, and basic meaning

• Structure: 矢先, read やさき, can mean the moment just as an action is about to occur or a literal arrowhead.
• Basic usage: 出ようとした矢先に marks an interrupted moment; 折れた矢先を取り替える refers to a physical arrowhead.

2. Common pitfalls and similar expressions

• Imminent moment and arrowhead
  • The attempted-action pattern selects the temporal sense; breaking and replacement select the physical object.