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innermost secrets (of an art or skill); mysteries; essence; heart
料理の極意は素材を活かすことだ。
The secret of cooking is to bring out the ingredients.
商売の極意を先代から学んだ。
He learned the secrets of business from the previous generation.
武道の極意に到達する者は稀だ。
Those who reach the innermost secrets of martial arts are rare.