Once a person went to an old zen master to learn the art and science of zen. The master asked the visitor if he would like to have a cup of tea since he must be tired having come from afar. The visitor happily said yes. The master made the tea and while he was pouring in the cup, the visitor suddenly noticed that the cup was full and the tea was overflowing. He almost shouted, "Master, the tea is falling". The master said, "This is the first lesson, I wanted you to learn. Unless the cup is empty, more tea will not come in it. The same applies to our minds. Unless we unlearn something from the past, we can not imbibe new knowledge."