sticking to one thing; single-mindedly; never deviating from
Idiomatic expression used after a noun to describe someone or something that is relentlessly focused on a single method, principle, or objective. Often carries a nuance of inflexibility or narrowness.
彼は金もうけ一本やりだ。
He is single-mindedly focused on making money.
That company has stuck to quality above all else.
one's sole talent; one's only forte
Refers to a person's single strong point or only skill. Often used self-deprecatingly or to describe someone with a narrow but deep ability.
Cooking is his one and only forte.
My only talent is waking up early.