tranquillite

One man is bound by high office, another by wealth; good birth weighs down some, and a humble origin others; some bow under the rule of other men and some under their own; some are restricted to one place by exile, others by priesthoods: all life is servitude. So you have to get used to your circumstances, complain about them as little as possible, and grasp whatever advantage they have to offer: no condition is so bitter that a stable mind cannot find some consolation in it.
—  Lucius Annaeus Seneca, De Tranquillitate Animi (On Tranquility of Mind)

Heraclitus wept whenever he went out in public, and Democritus laughed: the one thought all our behavior pitiful, the other silly. We ought to take the lighter view of these things and cultivate tolerance; it is more civilized to laugh at life than to lament over it. 

Further, the man who laughs at the human race deserves more gratitude than the man who mourns over it, for he allows it hope of amelioration, whereas the foolish weeper despairs of the possibility of improvement.

—  Lucius Annaeus SenecaDe Tranquillitate Animi (On the tranquility of the mind)
Let us get used to banishing ostentation, and get used to measuring things by their qualities of function rather than display. Let food banish hunger and drink banish thirst; let sex indulge its needs; let us learn to rely on our limbs, and to adjust our style of dress and our way of living not to the newfangled patterns but to the customs of our ancestors. Let us learn to increase our self-restraint, to curb luxury, to moderate ambition, to soften anger, to regard poverty without prejudice, to practice frugality, even if many are ashamed of it, to apply to nature’s needs the remedies that are cheaply available, to curb as if in fetters unbridled hope and a mind obsessed with the future, and to aim to acquire our riches from ourselves rather than from Fortune.
—  Lucius Annaeus Seneca, De Tranquillitate Animi (On Tranquility of Mind)