stubborn
Not willing to change your mind, even when you should.
Stubborn means refusing to change your mind or behavior, even when others try to convince you or when changing might be the smarter choice. A stubborn person digs in their heels and won't budge, like a mule that plants its feet and refuses to move no matter how much you pull on its reins.
Being stubborn can sometimes show determination and strength. If you're working on a difficult puzzle and refuse to give up, that stubbornness helps you succeed. But stubbornness becomes a problem when you won't listen to good advice or admit when you're wrong. If your friend points out a better route home and you insist on your way just because you already decided, that's unhelpful stubbornness.
The key difference is whether you're being stubborn about something that matters (like not giving up on learning to ride a bike) or just being stubborn for its own sake (like refusing to try a new food simply because you said you wouldn't). Stubborn people often say things like “I don't care what anyone says” or “I'm not changing my mind,” even when the evidence clearly points the other way.
Related words include obstinate, which means stubbornly refusing to change, and pigheaded, which suggests stubborn foolishness. When you're being wisely persistent, people call it determination. When you're being foolishly unchangeable, they call it stubbornness.