Mortimer Adler, How to Read a Book (p. 140):
Teachability is often confused with subservience.
A person is wrongly thought to be teachable if he is passive and pliable.
On the contrary, teachability is an extremely active virtue.
No one is really teachable who does not freely exercise his power of independent judgment. He can be trained, perhaps, but not taught. The most teachable reader is, therefore, the most critical. He is the reader who finally responds to a book by the greatest effort to make up his own mind on the matters the author has discussed.