The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts.—Bertrand Russell

According to an African proverb, when there is no enemy within, the enemy outside can do you no harm. If you think you can, if you think you can’t, you are also right. The battle is in the mind, to achieve your dreams and aspirations, you need to have unparalleled self-confidence in yourself. If you are competent and not confident, success would elude you but if you are competent and confident at the same time, you would become unstoppable.

If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours. – Henry David Thoreau

In the Seasons of Life, Jim Rohn writes:

Do not doubt yourself, for where doubt resides, confidence cannot. Do not neglect yourself, for with neglect comes loss. Do not imagine yourself to be less than you are, nor more than you are, but seek always to become all of which you are capable. Do not allow yourself to become arrogant or discourteous, for both are characteristics adopted by those who seek to cover their weaknesses.