Everyone gets disappointed. You get disappointed because you are touching the edges of reality. On the edge you see that everything you ever grasped vanishes. You don’t like it. You get frustrated. You feel thwarted. The real world gets your attention. This edgy place is the real world pulling on your sleeve.
When you feel disappointed with a bad teacher or a bad student, don’t run away. Stick with it. There’s no thing to depend on. Now, sit some more. Clean. Walk slowly. Pay attention. Bow and eat then wash your bowl.