Witness.

Among the principles readiest to thine hand, upon which thou shalt pore, let there be these two. One, that objective things do not lay hold of the soul, but stand quiescent without; while disturbances are but the outcome of that opinion which is within us. A second, that all this visible world changes in a moment, and will be no more; and continually bethink thee to the changes of how many things thou hast already been a witness. The Universe—mutation: Life—opinion.

Marcus Aurelius