Remember that man lives only in the present, in this fleeting instant; all the rest of his life is either past and gone, or not yet revealed. Short, … - Marcus Aurelius

Either all things proceed from one intelligent source and come together as in one body, and the part ought not to find fault with what is done for the benefit of the whole; or there are only atoms, and nothing else than a mixture and dispersion. Why, then, art thou disturbed? Say to this ruling faculty, Art thou dead, art thou corrupted, art thou playing the hypocrite, art thou become a beast, dost thou herd and feed with the rest?

Learn to ask of all actions, “Why are they doing that?” Starting with your own. (Hays translation)

Every being ought to do that which is according to its constitution; and all other things have been constituted for the sake of the superior, but the rational for the sake of one another.