Be (as) stubborn as a mule phrase informal simile
Be extremely stubborn
Mina is as stubborn as a mule. She doesn't like broccoli and she won't eat it even if you pay her.
She won't do what you tell because she's as stubborn as a mule.
The boy is as stubborn as a mule. He is bent on buying that motor.
Used to describe someone who is realistic and determined
The verb "be" should be conjugated according to its tense.
very excited and interested
Children are as keen as mustard to discover new things around them.