The most painful thing about a new idea coming across the mind, is the fact that the mind has never thought about that. When you come across such a thing you may want to act defensively. Such an idea threatens your old ways of living. That frightens you to dead. You have to go through the pain of redefining everything; forming new boundaries; becoming a child; learning from scratch. All of this is terrifying. You surely do not want any of those things. It is preceded by a very painful fact: All your previous believes might be false. This is unbearable for an unprepared mind. A mind that has never been open to the notion of new possibilities will barely survive such new ideas. 

We fear the unknown for in it might be hidden a painful truth.