“If you doubt you can accomplish something, then you can't accomplish it. You have to have confidence in your ability, and then be tough enough to follow through.”
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Rosalynn Carter 2
Wife of the 39th President of the United States, Jimmy Cart… 1927Related quotes

“If you have accomplished all that you have planned for yourself, you have not planned enough.”
In Quote, Unquote (1977) by Lloyd Cory, p. 6, this statement was simply attributed to the Meggido Message which is the name of a publication by the Meggido Church http://www.megiddo.com/, but immediately following a quote by Hale. This may have led to it being attributed to Hale in The Quotable Manager : Inspiration for Business and Life (2006) by Joel J. Weiss, p. 128; a similar expression "If you have achieved all you have planned for yourself, you have not planned enough" occurs in two works by John Mason: Let Go of Whatever Makes You Stop (1994), p. 79, and Know Your Limits — Then Ignore Them (2000), p. 123
Misattributed

Another excerpt from the Tris Speaker speech – featuring a much more familiar version of the "wasting your time" warning – as quoted in "Standing Cheer for Roberto" by Houston Chronicle sportswriter John Wilson, in The Sporting News (February 20, 1971), p. 44.
Other, <big><big>1970s</big></big>, <big>1971</big>
Context: We must all live together and work together no matter what race or nationality. If you have an opportunity to accomplish something that will make things better for someone coming behind you, and you don't do that, you are wasting your time on this earth.
“You have within you the potential to accomplish wonderful things with your life.”
The 21 Success Secrets of Self-made Millionaires (2001), Conclusion : Success Is Predictable, p. 64
Context: You have within you the potential to accomplish wonderful things with your life. Your greatest responsibilities are to dream big dreams, decide exactly what you want, make a plan to achieve it … take action every single day in the direction of your dreams and goals, and resolve to never, never, never give up. When you take these actions, you put yourself on the side of the angels. You become unstoppable and your success becomes inevitable.

Source: It Worked For Me: In Life and Leadership (2012), p. 23

The Meir Amit Intelligence and Terrorism Information Center, 22 August 2018 (date of quote)
2014, 2018, Statement released in Arabic, 22 August 2018
Source: In a public statement by ISIS leader Abu Bakr al Baghdadi, the first in a year, he calls on his supporters to carry out terrorist attacks worldwide, mainly in Western countries. He mentions shooting, stabbing and ramming attacks as well as detonation of IEDs. https://www.terrorism-info.org.il/en/microsoft-wordin-public-statement-isis-leader-abu-bakr-al-baghdadi-first-year-calls-supporters-carry-terrorist-attacks-worldwide-mainly-western-countries-ment/, The Meir Amit Intelligence and Terrorism Information Center, 27 August 2018