I found this great quote in the book Urban Shaman by Serge Kahili King, Phd. (A book I highly recommend – it is subtitled A Handbook for Personal and Planetary Transformation based on the Hawaiian Way of the Adventurer).
The quote is from CW Leadbeater: “It is the commonest of mistakes to consider that the limit of our power to perceive is also the limit of all there is to perceive.”