Who knows, but he might have had a bout of amnesia. Some mysterious force or figure might have stepped inside his head and completely removed every shred of his former memory without fair warning and seemingly without adequate reason (that is to say that any reason or warning would be, at the current juncture, forgotten to him anyway).
Immediately after the onset, he would have remained against the wall, bereft of he-would-not-know-what, and shifted his head slightly to the left, as if he were gently shaking water from his ear (although there would currently be no water in his ear, nor would he make the comparison of his physical movements to that of a man shaking water from his ear, as he would have no memory of having shaken water from his own ear or ever having observed the shaking of water from the ear of any other).
He might have a faint urge to get a cheeseburger, a giant one, though on this he may also be mistaken. He would be unsure as to whether he is a vegetarian. He would consider the possibilities.
And finally, peering around at the highway above him, the traffic, the garish swoop of concrete roadway, he might whisper softly to himself: "I want to change the world."
