Is there an idiom for the action when someone holds tightly onto his opinion? Like you keep to try convincing that person again and again but he keeps that opinion?
"He/she dug his heels in"
is often used to convey a specific act of stubbornness or defiance.
Or, if it is specific to the fact the person seems unwilling to hear what you are saying:
"I tried to explain to them, but they are just tone deaf to my ideas"
(they are not really deaf; it is just a metaphorical way of saying that they refuse to listen).
Stubborn as a mule and obstinate as a mule may convey the idea:
- Cliché very stubborn. (*Also: as ~.) I tried to convince Jake to go to the doctor, but he's as stubborn as a mule. For four years, Henry pestered his parents to let him learn the trumpet. They tried to talk him into some other, quieter instrument, but he was stubborn as a mule, and now he has a trumpet.
The phrase whim of iron has been used to describe a stubbornness that lacks a reasonable basis.
It i attributed to Oliver Herford (December 3, 1863 – July 5, 1935), an American humorous poet and illustrator. Wikiquote
The Middle English version of stubborn carried the sense of “untamable, implacable,” and there’s still a hint of that in how it is used today.
Few suggestions: Unbend (verb) means 'to change from a bent position, to straighten', and also 'to relax from stress or severity'. By contrast, the adj. unbending normally means 'unyielding, inflexible;
You can also use resistant or resistance depending on how you mean stubborn.
Lexico defines resistant:
Offering resistance to something or someone.
‘some of the old Churches are resistant to change’