肝心

1. Origins, structure, and basic meaning

• Structure: 肝心 (かんじん) is a noun and na-adjective for what is essential or most important among several factors.
• Basic usage: 肝心の modifies a crucial noun, while ことが肝心だ identifies an action or point as key.
  • 道具はそろったのに、肝心の材料を忘れました。 — We had all the tools but forgot the most important material.
  • 練習を続けるには、楽しむことが肝心です。 — Enjoyment is the key to continuing practice.

2. Common pitfalls and similar expressions

• Important and the crucial point
  • 重要 broadly means important, while 肝心 strongly marks the crucial element that must not be missed in the immediate situation.