How do you know you can succeed - your instinct makes you aware. Now, believe this or not: every man is born with a desire to succeed. Even to the extent that some people assume "life is a race." Its believe to be 'the survival of the fittest.'
An illustration below will give a better insight:
In a marathon race. Every racer steps on the field with an ambition. A desire to come first. Nobody wants to be the last. Infact, known of them think such. However, someone will make the last position.