How is grendel "caged in a limited mind"?

Grendel caged in a limited mind because he only knows his own experiences or what happened to him or what he do in his life.

If we listen to other peoples experience, we come to know many new things and obviously life is beautiful and every person have different experiences in their life. Some people have bad experiences and some people have good. By knowing and listening to other people, we were not caged in a limited mind we become open minded.