I have before me a packet of dehydrated onions.

   Let these dried onions stand for something which has been written down. They are neither the original experience (the onion) nor are they nothing at all. They possess a virtuality.

   Add hot water, and this is absorbed by your dried material. After a few minutes, we have something which we know to have been dried onions, but which is not now the same. What we now have is 'reconstituted onions.'

   We do not have whole onions, it is true. Neither do we have fresh onions. But we have something which will enable us to recognize fresh onions when we see and taste them. This is an advance upon dried onions. 

   The original experience was fresh onions. The water was the addition made by the right circumstances of study. The result is edible, and this is a suitable substitute for fresh onions. It contains some nutrition, too.

   Those who say: 'You cannot make anything out of dried onions' -- the equivalent of 'You cannot get anything from a book' -- are wrong. Those who say: 'I will wait (or search) until I find fresh onions' are wrong. They are wrong because they do not realize that they would not recognize 'fresh onions' if they saw them. This has to be said, though reluctantly, because such statements are usually taken as challenging, when they are more often intended only to be descriptive. 

   Let us therefore postulate the statement: 'You can get something from a book.  That something may be so important as to lead you to the recognition of the real thing. It is therefore in many cases all-important.'

From Idries Shah book: Learning How to Learn