What we speak nowadays corresponds little to outward facts. It is mostly the outcome of various opinions and passions. However, when we add to our external sensory perceptions what does not match pure reality, and reflect it as thoughts, we destroy our capacity for higher knowledge. […] The most basic rule for ascending to the higher worlds is this: learn to hold on to the pure facts of the physical world.
Source (German): Rudolf Steiner – GA 220 – Lebendiges Naturerkennen Intellektueller Sündenfall und spirituelle Sündenerhebung– Dornach, January 20, 1923 (page 128-129)