Success comes wherever there is sincerity and effort. It has nothing to do with our inner or outer beliefs. I have seen genuine, sincere workers, successful people in both believers and non-believers. Theism and Atheism stand very much on the same level of ignorance. Spiritual seeking goes beyond beliefs and non-beliefs. Many theists are believers by default. They adopt the beliefs and religion of the family they are born in. This belief, on the one hand provides them a framework to operate, a comfort zone to cushion and a support system of believers of the common faith. But its big disadvantage is that often it kills or stifles seeking, often a mechanical and unthinking acceptance of the dogmas of the belief system they are born in. Thus it blocks the path of spiritual progress. On the other hand the Atheist has no such ready made comfort zones and hence he relies on effort and skills and his only instrument Reason. But he too blocks his spiritual seeking by an excessive reliance on reason that relies heavily on sensory data. But since he relies on personal effort lot more he does increase his chances of success.
Affectionately,
Alok Da