The universe is flux, life is opinion.
The universe is transformation: life is opinion. (Long translation)
ὁ κόσμος ἀλλοίωσις, ὁ βίος ὑπόληψις.
IV, 3
Variant: Our life is what our thoughts make it.
Source: Meditations (c. 121–180 AD), Book IV

“Because a thing seems difficult for you, do not think it impossible for anyone to accomplish.”

Marcus Aurelius

Source: The Meditations of the Emperor Marcus Aurelius Antoninus

“How much more grievous are the consequences of anger than the causes of it.”

Marcus Aurelius book Meditations

Source: Meditations (Promluvy k sobě)

“Persevere then until thou shalt have made these things thy own”

Marcus Aurelius book Meditations

X, 31
Meditations (c. 121–180 AD), Book X
Context: What matter and opportunity [for thy activity] art thou avoiding? For what else are all these things, except exercises for the reason, when it has viewed carefully and by examination into their nature the things which happen in life? Persevere then until thou shalt have made these things thy own, as the stomach which is strengthened makes all things its own, as the blazing fire makes flame and brightness out of everything that is thrown into it.

“He who follows reason in all things is both tranquil and active at the same time, and also cheerful and collected.”

Marcus Aurelius book Meditations

X, 12
Meditations (c. 121–180 AD), Book X
Context: What need is there of suspicious fear, since it is in thy power to inquire what ought to be done? And if thy seest clear, go by this way content, without turning back: but if thy dost not see clear, stop and take the best advisers. But if any other things oppose thee, go on according to thy powers with due consideration, keeping to that which appears to be just. For it is best to reach this object, and if thou dost fail, let thy failure be in attempting this. He who follows reason in all things is both tranquil and active at the same time, and also cheerful and collected.

“There are three relations [between thee and other things]:”

Marcus Aurelius book Meditations

VIII, 27
Meditations (c. 121–180 AD), Book VIII
Context: There are three relations [between thee and other things]: the one to the body which surrounds thee; the second to the divine cause from which all things come to all; and the third to those who live with thee.

“For what else are all these things, except exercises for the reason”

Marcus Aurelius book Meditations

“Accept the things to which fate binds you, and love the people with whom fate brings you together, but do so with all your heart.”

Marcus Aurelius book Meditations

Source: Meditations

“Things have no hold on the soul. They have no access to it, cannot move or direct it. It is moved and directed by itself alone. It takes the things before it and interprets them as it sees fit.”

Marcus Aurelius book Meditations

Hays translation
V, 19
Meditations (c. 121–180 AD), Book V

“Love the little trade which thou hast learned, and be content therewith.”

Marcus Aurelius book Meditations

IV, 31
Meditations (c. 121–180 AD), Book IV

“No matter what anyone says or does, my task is to be good.”