One famous quote of encouragement is: "Go confidently in the direction of your dreams. Live the life you have imagined," by Henry David Thoreau. Another example is: "Trust yourself. You know more than you think you do," by Benjamin Spock.
Encouraging words and quotes can be helpful during times of struggle. They help people learn from others who have traveled a similar road and found wisdom and success in the process.
One more example of a famous encouraging quote is: "When one door closes another door opens; but we so often look so long and so regretfully upon the closed door, that we do not see the ones which open for us," by Alexander Graham Bell.