stubborn
倔 centers on an unyielding, stubborn attitude: a person who is strong-willed and refuses to bend or change.
倔 combines the person radical 亻 with 屈 (bend, yield). The character likely expresses a person who does not yield, i.e., stubborn. The exact historical development is uncertain.
A person 亻 who is bent 屈 in their ways: so set in their posture that they refuse to straighten out. That's a stubborn person.
For クツ, imagine a stubborn person who refuses to wear shoes (靴, くつ) even when it's cold. Their stubbornness is as hard as a boot: くつ -> クツ.