Our Gemara on Amud Aleph quotes a verse from Mishlei (10:25):
כַּעֲב֣וֹר ס֭וּפָה וְאֵ֣ין רָשָׁ֑ע וְ֝צַדִּ֗יק יְס֣וֹד עוֹלָֽם׃
"When the storm passes the wicked man is gone, But the righteous is an everlasting foundation."
While there are various interpretations, the simple meaning of the verse suggests that the righteous possess a certain stability and are not disoriented or disrupted by the occasional storms of life. This speaks to a state of mind characterized by calmness, openness, acceptance, optimism, and faith.
In Mussar literature, this state is known as hishtavus, which can be translated as equanimity. Chovos Halevavos (Shaar Yichud HaMasechah 2:8) states:
שיהיה שוה אצלו אם ישבחוהו בני אדם או יגנוהו.
"That one should be equal within oneself whether people praise or scorn him."
The Tzava'a of the Baal Shem Tov also speaks of equanimity, playing on the words from the verse "שויתי ה' לנגדי תמיד," meaning that one's awareness of God allows everything else to be put into perspective, without being rattled or disturbed.
It seems that many philosophical and religious systems recognize this state of human calmness, peace, and receptivity. The Amish refer to it as Gelassenheit, which signifies self-surrender and resignation to God's will, yielding oneself to God's will, or passive openness to God's will with peace and tranquility of mind. Similarly, there is the ancient Chinese concept of Wu Wei, which literally means "inexertion," "inaction," or "effortless action." It represents a state of personal harmony, free-flowing spontaneity, and laissez-faire.
Chapter II of the Tao Te Ching states:
The Sage is occupied with the unspoken and acts without effort. Teaching without verbosity, producing without possessing, creating without regard to result. Claiming nothing, the Sage has nothing to lose.
An interesting Zen parable bears similarities to the Mussar ideal of hishtavus and even Gam Zu Letova. It goes as follows:
One day in late summer, an old farmer was working in his field when a beautiful wild stallion wandered onto his field. He was successful in capturing it.
Word got out in the village of the old farmer's good fortune, and people stopped by to congratulate him on his luck. "How fortunate you are!" they exclaimed. "You must be very happy!" Once again, the farmer calmly said, "Who knows? We shall see."
The following day, the farmer's son attempted to train the wild horse but was thrown to the ground, breaking his leg. Villagers arrived throughout the day to bemoan the farmer's misfortune. "Oh, what a tragedy! Your son won't be able to help you farm with a broken leg. How will you survive? You must be very sad," they said. Serenely going about his usual business, the farmer replied, "Who knows? We shall see."
Several days later, a war broke out, and the Emperor's men arrived in the village to conscript young men. The farmer's son was deemed unfit due to his broken leg. "What good fortune you have!" the villagers exclaimed as their own sons were taken away. "You must be very happy." Once again, the farmer replied, "Who knows? We shall see!" as he headed off to work his field alone.
As time went on, the son's leg healed, but he was left with a slight limp. The neighbors came to pay their condolences, saying, "Oh, what bad luck. Too bad for you!" The old farmer simply replied, "Who knows? We shall see."
As it turned out, the other young village boys had died in the war, and the old farmer and his son were the only able-bodied men capable of working the village lands. The old farmer became wealthy and generously supported the villagers. They said, "Oh, how fortunate we are. You must be very happy." To this, the old farmer replied, "Who knows? We shall see!"
This Zen story illustrates the value of the Mussar attribute of hishtavus, or equanimity. It emphasizes the idea that a person should accept both apparent misfortune and apparent fortune with composure and temper their reactions.
The fact that different religious and philosophical systems place value on and exemplify this mental and psychological state indicates an intuitive awareness of its unique value, as well as the attainability of this healthy mindset.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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