I feel that no one is born great. The achievement of greatness is within a person and is established by his/her foundation of choices and of course it is developed by the series of events that occurred around him/her at the time.
With Einstein, I believe the foundation of choice stemmed from his inability to be successful in certain areas of academia. The circumstances at hand, pushed him to think outside the box and find answers to questions that had probably not been asked. Why? Probably because he was bored. He found something that no one else had conquered and developed processes and theories that would allow results.
As he grew older and began to display his achievement of greatness through multiple publications of research and development, the necessity of his answers caused greatness. Einstein was not understood by his peers in the area of physics. Therefore the demand for his skills and abilities would have been a catapult of his greatness. Of course the introduction of atomic energy into the picture was also a 'thrust' into the arena of greatness.
Einstein achieved greatness through his determination and genius intellect. Einstein was thrust into greatness by the demands of first, his learning disability and then second, the need for his genius by various institutions and governments.