Happy the man who can endure the highest and the lowest fortune. He, who has endured such vicissitudes with equanimity, has deprived misfortune of its power.
— Marcus Annaeus Seneca Seneca The Elder

Few people are capable of expressing with equanimity opinions which differ from the prejudices of their social environment. Most people are even incapable of forming such opinions.
Albert Einstein equanimity quote

When force of circumstance upsets your equanimity, lose no time in recovering your self-control, and do not remain out of tune longer than you can help. Habitual recurrence to the harmony will increase your mastery of it.
— Marcus Aurelius

Even a happy life cannot be without a measure of darkness, and the word happy would lose its meaning if it were not balanced by sadness. It is far better take things as they come along with patience and equanimity.
— Carl Jung

So nothing is ever good or bad unless you think it so, and vice versa. All luck is good luck to the man who bears it with equanimity.
— equanimity quotation by Boethius (Anicius Manlius Severinus)