Years ago I read a quote that basically said that you could tell an truly intelligent person something and they would learn from it but you couldn't tell someone something if they already thought they knew it all and it disagreed with their way of thinking. Of course, the quote put it so much better than this, which is why I'd really like to find it.

I hope that this is the one you are looking for -

"I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of their conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread into the fabric of their lives."
~Tolstoy

There is a zen saying, or thought, which I am about to butcher marvelously. The saying is: "Empty your cup first."

It simply refers to the idea that if your mind is like a full cup of tea, no new ideas will go in to it. There is no room for anything more. However if you empty your cup (your mind) of preconceived ideas and attitudes, you will be able to receive new ones.

Petrarchs statement of the zen saying reminded me of a story that had more or less the same point. I forget the exact context, but a reporter of some kind was going to interview a priest on the subject of zen. He made some comment to that effect, and the priest nodded gravely, and began pouring himself a cup of tea. However, when the cup was full he kept pouring, and the tea was overflowing the sides of the cup. The reporter watched with disbelief, until he couldn't stand it any longer, and said, "Stop! The cup is full, you can't pour any more in."

The priest smiled, and said, "Your mind is like this cup. Unless you empty it of its preconcieved notions of Zen, I cannot teach you anything about it."

I forget where I heard this story, though.