There are two kinds of understanding: negative and positive. On the positive side, individuals are omniscient, and personal feelings are everything; On the negative side, I am ignorant and know nothing about objective existence, only my own feelings. We believe that the latter is an ancient tendency, while the former is a tendency that only appeared in modern times. We can see from the ancients' simple understanding of feelings, such as empedocles's flow theory and democritus's image theory, that in the minds of these ancients, our feelings are different from real objects, and they have changed through natural links such as sensory organs and air. Therefore, the thought of "God is unknowable" is a summary of protagoras's latent thought of "flowers are unknowable", and it is also the continuation and development of democritus's insensitive thought of "atom".