Success never comes down to just one thing. Intelligence, talent, experience, education, and even luck all play their part. But often what separates success from failure is perseverance. Keep going and you still have a chance to succeed; quit, and all hope of success is lost.

Even so, when things get difficult and the odds of success seem bleak, doubt naturally sets in, and slowly -- although sometimes very quickly -- drains away your willpower, determination, and motivation.