Meditations, Book 10, Section 19

Marcus Aurelius — The Emperor

Always remind yourself of this: picture the vast age of the world and all of existence. See how small each particular thing is compared to the whole — like a tiny seed. See how brief each thing lasts — like one turn of a pestle in a mortar. Then look at any object around you. See it as it really is: already breaking down and changing. Everything tends toward decay or scattering. This is the natural death that comes to all things of its kind.

Marcus Aurelius — The Emperor Original

Ever to represent unto thyself; and to set before thee, both the general age and time of the world, and the whole substance of it. And how all things particular in respect of these are for their substance, as one of the least seeds that is: and for their duration, as the turning of the pestle in the mortar once about. Then to fix thy mind upon every particular object of the world, and to conceive it, (as it is indeed,) as already being in the state of dissolution, and of change; tending to some kind of either putrefaction or dispersion; or whatsoever else it is, that is the death as it were of everything in his own kind.