slippery

 slippery:

 causing or tending to cause objects to slip 

 liable to slip from the grasp, a position, etc.

 not to be relied upon

 liable to change; unstable

An ardent Jehovah's Witness once tried to convince me
 that if there were a God of love, he would certainly provide mankind
 with a reliable and infallible textbook for the guidance of conduct.

 I replied that no considerate God would destroy the human mind 
by making it so rigid and unadaptable as to depend upon one book,
the Bible, for all the answers. For the use of words, and thus of a book,
 is to point beyond themselves to a world of life and experience
 that is not mere words or even ideas. Just as money is not real, 
consumable wealth, books are not life. To idolize scriptures
 is like eating paper currency.

Therefore the Book that I would like to slip to my children
 would itself be slippery. It would slip them into a new domain, 
not of ideas alone, but of experience and feeling. It would be a temporary
 medicine, not a diet; a point of departure, not a perpetual
 point of reference. They would read it and be done with it, 
for if it were well and clearly written they would not have to go back
 to it again and again for hidden meanings or for
 clarification of obscure doctrines.

~ Alan Watts

from The Book on The Taboo against knowing who you are