When engaged in thinking, he should definitely exclude all thoughts connected with the phenomena of sight, sound, taste, smell, touch, and all discriminations based upon them, keeping his thinking independent of all such arbitrary conceptions of phenomena. The mind is disturbed by these discriminations of sense concepts and the following arbitrary conceptions about them and, as the mind becomes disturbed, it falls into false imaginations as to one's self and its relation to other selves. It is for that reason that the Tathagata has constantly urged the Bodhisattva-Mahasattvas in their practice of charity not to be influenced by any arbitrary conceptions of phenomena such as sights, sounds, etc.

(The Maha Prajna Paramita)