set in one's ways

Adjective

idiomatic

(idiomatic) Driven by habit; inclined or determined to continue according to one's custom or established preferences.

Japanese Meaning

決まった習慣ややり方に固執して、なかなか変えようとしないこと / 自身の決まった習慣に従い、変化に抵抗する性質があること / 長年の習慣・固定観念に縛られて新しい方法に適応しにくいという性向

A person who is set in one's ways will rarely change habits, even when a new routine would help.

習慣に固執する人は、新しいやり方が役立つときでもほとんど習慣を変えません。

Sense（1）

(idiomatic) Driven by habit; inclined or determined to continue according to one's custom or established preferences.

He's as set in his ways now as a little old man.