Question on Macbeth🤔

First is, why couldn’t he make his own right decision? And sticked with “no I’m not going to kill the king” to his wife.

He knows it’s the wrong thing to do to kill the king, why still proceed with it. Is he not suppose to be a fearsless warrior? Clearly he knows that it will lead to a really bad consequence and karma will come back to him and bite him. He had this conversation with himself before.