As quoted in The Ring of Truth (2004) by Joseph O'Day
Positive quotes
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“Extraordinary things are always hiding in places people never think to look.”
Source: My Sister's Keeper
“The difference between ordinary and extraordinary is that little extra.”

“The road to success is always under construction”

“The more you praise and celebrate your life, the more there is in life to celebrate.”
“People rarely succeed unless they have fun in what they are doing.”
Dale Carnegie, quoted in Permission to Play : Taking Time to Renew Your Smile (2003) by Jill Murphy Long, p. 69

“I never lose sight of the fact that just being is fun.”

“Write it on your heart that every day is the best day in the year.”
Works and Days
1870s, Society and Solitude (1870)

“The POSITIVE THINKER sees the INVISIBLE, feels the INTANGIBLE, and achieves the IMPOSSIBLE.”
Source: My Early Life, 1874-1904

"Proclamation 3560 — Thanksgiving Day, 1963" (5 November 1963) http://www.presidency.ucsb.edu/ws/?pid=9511<!-- Online by Gerhard Peters and John T. Woolley, The American Presidency Project -->
1963
Context: Today we give our thanks, most of all, for the ideals of honor and faith we inherit from our forefathers — for the decency of purpose, steadfastness of resolve and strength of will, for the courage and the humility, which they possessed and which we must seek every day to emulate. As we express our gratitude, we must never forget that the highest appreciation is not to utter words but to live by them.
Let us therefore proclaim our gratitude to Providence for manifold blessings — let us be humbly thankful for inherited ideals — and let us resolve to share those blessings and those ideals with our fellow human beings throughout the world.

“To know even one life has breathed easier because you have lived. This is to have succeeded.”

“Even if you are on the right track, you’ll get run over if you just sit there.”
Variant: Even if you are on the right track, you will get run over if you just sit there.

“Yesterday is not ours to recover, but tomorrow is ours to win or lose.”
“A year from now you may wish you had started today.”

“Optimism is the faith that leads to achievement; nothing can be done without hope.”
Optimism (1903)
Variant: Optimism is the faith that leads to achievement

“For every minute you are angry you lose sixty seconds of happiness.”
No known source in Emerson's works; first found as a piece of anonymous folk-wisdom in a 1936 newspaper column:
: Every minute you are angry, you lose 60 seconds of happiness.
:* Junius, "Office Cat" https://www.newspapers.com/newspage/85995624/, The Daily Freeman [Kingston, NY] (30 December 1936), p. 6
Misattributed

“You cannot have a positive life and a negative mind.”
Source: Battlefield of the Mind: Winning the Battle in Your Mind

“If I cannot do great things, I can do small things in a great way”

“Perpetual Optimism is a Force Multiplier.”

Oh, the Places You'll Go! (1990)
Source: Oh, The Places You'll Go!
“It is better for the heart to break, than not to break.”

“A problem is a chance for you to do your best.”
Source: Music is My Mistress

“Success is getting what you want.
Happiness is wanting what you get.”

“It makes a big difference in your life when you stay positive.”
Source: Seriously... I'm Kidding

“The more I want to get something done, the less I call it work.”
Illusions : The Adventures of a Reluctant Messiah (1977)
“Positive expectations are the mark of the superior personality.”
Source: Maximum Achievement: Strategies and Skills that Will Unlock Your Hidden Powers to Succeed
“it's wrong to be right; it's right to be wrong.”

“T is what you will,—or will be what you would.”
First Week, Third Day.
La Semaine; ou, Création du monde (1578)

“The more you know, the less you are.”
1960's, Conversations with Samuel Beckett and Bram van Velde' (1965 - 1969)

“You are never too old to set another goal, or to dream a new dream.”
Unknown, but also attributed to Les Brown, a motivational speaker. Commonly attributed to C.S. Lewis, but never with a primary source listed.
Misattributed

"A letter to Canadians from the Honourable Jack Layton." https://pdf.yt/d/RKyhnDdu-DXG3J6s 20 August 2011.
Released upon his death.

“Either you will be you or you will not be at all.”
“The Knight,” p. 81
The Sun Watches the Sun (1999), Sequence: “What After”

“Life is everything and nothing all at once.”
From the Pisces Iscariot liner notes.

“All our dreams can come true — if we have the courage to pursue them.”
Source: How to Be Like Walt : Capturing the Magic Every Day of Your Life (2004), Ch. 3 : Imagination Unlimited, p. 63; Unsourced variant: All your dreams can come true if you have the courage to pursue them.

“Success is a state of mind. If you want success, start thinking of yourself as a success.”
As quoted in The Pocket Philosopher/ Psychologist (2004) by Mark J. Merten, p. 87
The Four Agreements (1997)

Source: 1900s, Up From Slavery (1901), Chapter XI: Making Their Beds Before They Could Lie On Them

As quoted in Edison & Ford Quote Book (2003) edited by Edison & Ford Winter Estates.
Date unknown

“I have not failed. I've just found 10,000 ways that won't work.”
As quoted in: [J. L.] Elkhorne. Edison — The Fabulous Drone, in 73 Vol. XLVI, No. 3 (March 1967) http://www.arimi.it/wp-content/73/03_March_1967.pdf, p. 52
Disputed

“The most positive men are the most credulous…”
Thoughts on Various Subjects (1727)

Bell Telephone Talk (1901)

“Failure is the condiment that gives success its flavor.”
From "Self-Portrait" (1972)
Truman Capote: Conversations (1987)

“There is no way to happiness; happiness is the way.”
The source is likely to be either modern Buddhist monk Thich Nhat Hanh, or Calvinist clergyman Abraham Johannes Muste. The phrase appears in Thich Nhat Hanh's writings; but it also appears in a volume of US senate hearings from 1948, when Thich Nhat Hanh had not yet been ordained as a monk. Muste is known to have used a variant of the phrase – "'peace' is the way" in 1967, but this was not the first time he had used it, and he had a connection with the 1948 hearing.
Misattributed

“No matter what people tell you, words and ideas can change the world.”

“It’s not whether you get knocked down, it’s whether you get up.”

“Positive thinking must be followed with positive doing.”
Book Sometimes you win Sometimes you Learn

“And you do not think that this is possible?”
“I’ll believe in anything when I see evidence for it.”
Chapter 12 (p. 188)
Terminal World (2010)

“If you change the way you look at things, the things you look at change.”

“A strong, positive self – image is the best possible preparation for success”

“Your smile will give you a positive countenance that will make people feel comfortable around you.”

“It's a wonderful thing to be optimistic. It keeps you healthy and it keeps you resilient.”

“Happiness is when what you think, what you say, and what you do are in harmony.”

“It always seems impossible until it's done.”

“Setting goals is the first step in turning the invisible into the visible.”

“Coming together is a beginning; keeping together is progress; working together is success.”

“The mind is everything. What you think you become.”

“Correction does much, but encouragement does more.”

“There is nothing in a caterpillar that tells you it's going to be a butterfly.”