The problem is, a discussion of the subject goes beyond the scope of a chat room like FR. You need to write a 5000 word essay on the subject.
First, you would have to determine if it is based on a single characteristic or a multitude of characteristics, some that were present in the beginning, and others that were added over time.
Some say it is our Puritan roots which can be broken into 2.
Delayed gratification, which we revere, while we frown on instant gratification. Secondly, the Shining City on the Hill was Puritan founding principle which came from the Sermon on the Mount, though we are not exactly sure who wrote that.
And others could point to our educational system. In the shift from an ag economy to an industrial economy, the educational system we developed played a big role in the nations success. Some people are uncomfortable with this subject because our educational system is highly socialistic, or it might not be adequate as we shift into an information technology economy.
You could go on and on and on and on. Some of these characteristics can be on the fringe: Exceptionalism could be based on hybrid vigor which is the result of a highly hybridized population. I always thought that I was very exceptional person because my father was a Vermont Yankee and my mother was a Mississippi Belle, and I grew up on the bunch grass prairies of west Texas. Nature and nurture.
Here is my 5000 word essay about American exceptionalism.
freedom