The relationship between commitment and doubt is by no means an antagonistic one. Commitment is healthiest when it's not without doubt but in spite of doubt.

Commitment is a quality which can be shown by all kinds of people. A person who is determined to achieve something does not get scared even if he has to work harder than others. He is confident that he can accomplish his goals. This kind of person does not hesitate to accept challenges which he may ... not be able to conquer at the first try. He is someone who will not let his work go for a moment. If he wants to achieve something, he will not rest until he does. He will go beyond the normal boundaries and is ready to make great efforts to achieve his goal. A person with commitment can be anyone. You can be a regular student who works hard for his exams, or a young girl who is determined to achieve her dreams. The key is to have the right kind of mindset. You have to be committed to the things that you want to achieve in life. If you are not, you are probably the one who is wasting his time.