Positive quotes

„There is no way to happiness. Happiness is the way.“

—  Thich Nhat Hanh Religious leader and peace activist 1926

„You cannot change what you are, only what you do.“

—  Philip Pullman, book Northern Lights

Source: His Dark Materials, The Golden Compass (1995), Ch. 18 : Fog and Ice

„The good life is a process, not a state of being. It is a direction not a destination.“

—  Carl R. Rogers American psychologist 1902 - 1987

Person to person: The problem of being human: A new trend in psychology (1967)
Source: page 187.

„When you change the way you look at things, the things you look at change.“

—  Max Planck German theoretical physicist 1858 - 1947

„There are years that ask questions and years that answer.“

—  Zora Neale Hurston, book Their Eyes Were Watching God

Source: Their Eyes Were Watching God (1937), Ch. 3, p. 21.

„Try to be a rainbow in someone's cloud.“

—  Maya Angelou, book Letter to My Daughter

Variant: Be a rainbow in somebody else's cloud.
Source: Letter to My Daughter

„Keep your face always toward the sunshine – and shadows will fall behind you.“

—  Walt Whitman American poet, essayist and journalist 1819 - 1892

This has become attributed to both Walt Whitman and Helen Keller, but has not been found in either of their published works, and variations of the quote are listed as a proverb commonly used in both the US and Canada in A Dictionary of American Proverbs (1992), edited by Wolfgang Mieder, Kelsie B. Harder and Stewart A. Kingsbury.
Misattributed

„The best way to cheer yourself is to try to cheer someone else up.“

—  Mark Twain American author and humorist 1835 - 1910

Variant of this quote "The best way to cheer yourself is to cheer somebody else up." is misattributed to Albert Einstein.
Source: According Quote Investigator Mark Twain did write a version of this saying in a personal notebook in 1896, and it was published by 1935 in “Mark Twain’s Notebook”. https://quoteinvestigator.com/2012/12/21/cheer-somebody/

„The power of imagination makes us infinite.“

—  John Muir Scottish-born American naturalist and author 1838 - 1914

1 September 1875, page 226
John of the Mountains, 1938
Context: How infinitely superior to our physical senses are those of the mind! The spiritual eye sees not only rivers of water but of air. It sees the crystals of the rock in rapid sympathetic motion, giving enthusiastic obedience to the sun's rays, then sinking back to rest in the night. The whole world is in motion to the center. So also sounds. We hear only woodpeckers and squirrels and the rush of turbulent streams. But imagination gives us the sweet music of tiniest insect wings, enables us to hear, all round the world, the vibration of every needle, the waving of every bole and branch, the sound of stars in circulation like particles in the blood. The Sierra canyons are full of avalanche debris — we hear them boom again, for we read past sounds from present conditions. Again we hear the earthquake rock-falls. Imagination is usually regarded as a synonym for the unreal. Yet is true imagination healthful and real, no more likely to mislead than the coarser senses. Indeed, the power of imagination makes us infinite.

„You cannot protect yourself from sadness without protecting yourself from happiness.“

—  Jonathan Safran Foer Novelist 1977

„If I got rid of my demons, I’d lose my angels.“

—  Tennessee Williams American playwright 1911 - 1983

Source: Conversations with Tennessee Williams

„We must embrace pain and burn it as fuel for our journey“

—  Kenji Miyazawa Japanese poet and author of children's literature 1896 - 1933

„Life is like riding a bicycle. To keep your balance you must keep moving.“

—  Albert Einstein German-born physicist and founder of the theory of relativity 1879 - 1955

Letter to his son Eduard (5 February 1930), as quoted in Walter Isaacson, Einstein: His Life and Universe (2007), p. 367
1930s

„Always turn a negative situation into a positive situation.“

—  Michael Jordan American retired professional basketball player and businessman 1963

„You get in life what you have the courage to ask for.“

—  Oprah Winfrey American businesswoman, talk show host, actress, producer, and philanthropist 1954

„We must be willing to let go of the life we planned so as to have the life that is waiting for us.“

—  Joseph Campbell American mythologist, writer and lecturer 1904 - 1987

Variant: You must give up the life you planned in order to have the life that is waiting for you.

„First say to yourself what you would be; and then do what you have to do.“

—  Epictetus philosopher from Ancient Greece 50 - 138

Book III, ch. 23.
Discourses
Original: (el) Τίς εἶναι θέλεις, σαυτῷ πρῶτον εἰπέ: εἶθ' οὕτως ποίει ἃ ποιεῖς.

„I would rather die of passion than of boredom.“

—  Emile Zola, book Au Bonheur des Dames

Source: The Ladies' Paradise

„Find a place inside where there's joy, and the joy will burn out the pain.“

—  Joseph Campbell American mythologist, writer and lecturer 1904 - 1987

Variant: Find a place inside where there's joy, and the joy will burn out the pain.