The important thing is how we handle those doubts. Rather than waste time fretting about his inadequacies, a successful man is able to set them far enough aside to act and improve. He knows that small triumphs pave the way for bigger ones. By getting up an hour earlier in the morning, you get a jump on others and add more than 15 productive days to your year. Don't demand perfection of yourself every time.
Success is a matter of the right effort for the right situation.
Celebrate a little when you get a pat on the back. Learning CPR or lifesaving techniques. You'll feel more competent even if you don't get the chance to save a life. Listen to you children, and let them know when you're proud. It may be hard to find the time, but you'll get back more than you give seeing the world from another man's shoes.