A person who doubts himself is like a man who would enlist in the ranks of his enemies and bear arms agains himself. He makes his failure certain by himself being the first person to be convinced of it.
Men of extraordinary success, in their honest moments, have always sung, "Not unto us, not unto us." According to the faith of their times, they have built altars to Fortune, or to Destiny, or to St. Julian. Their success lay in their parallelism to the course of thought, which found in them an unobstructed channel; and the wonders of which they were the visible conductors seemed to their eye their deed.
I've come to embrace the notion that I haven't done enough in my life. I've come to confirm that one's title, even a title like president of the United States, says very little about how well one's life has been led. No matter how much you've done or how successful you've been, there's always more to do, always more to learn, and always more to achieve.
The talent of success is nothing more than doing what you can do well, and doing well whatever you do without thought of fame. If it comes at all it will come because it is deserved, not because it is sought after.
On occasion we need to make a second effort - and a third effort, and a fourth effort, and as many degrees of effort as may be required to accomplish what we strive to achieve.