One aspect has to do with the inability of the sense-organs to record the facts of the outer world with perfect precision. These organs are the result of untold ages of evolution, and, generally speaking, have become wonderfully efficient, but they display surprising inaccuracies.
These inaccuracies are called Sensory Illusions.
Practical Aspects of Perception Process
The other aspect of the Sense-Perceptive Process has to do with the mental interpretation of environment.
Both these aspects are distinctly practical.
You should know something of the weaknesses and deficiencies of the sense-perceptive organs, because all your efforts at influencing other men are directed at their organs of sense.
You should understand the relationship between your mind and your environment, since they are the two principal factors in your working life.
SENSORY ILLUSIONS AND SUGGESTIONS FOR THEIR USE