Faith
Sometimes, it worried Sam that everyone had so much faith in him, especially during the times when Sam had absolutely no confidence in his abilities.
He knew, of course, that it had only been through that faith that he had managed to accomplish so much, made it so that even a nobody from Tranquility could make the impossible a reality.
Still, he feared that one day the impossible would remain impossible, that the burden would prove to be too much for him, and everyone would realize what a monumental mistake they had made for believing in him.