Tony Schwartz, the author of The Art of the Deal wrote:

“Trump has been written about a thousand ways from Sunday, but this fundamental aspect of who he is doesn’t seem to be fully understood,” Schwartz told me. “It’s implicit in a lot of what people write, but it’s never explicit—or, at least, I haven’t seen it. And that is that it’s impossible to keep him focussed on any topic, other than his own self-aggrandizement, for more than a few minutes, and even then . . . ” Schwartz trailed off, shaking his head in amazement. He regards Trump’s inability to concentrate as alarming in a Presidential candidate. “If he had to be briefed on a crisis in the Situation Room, it’s impossible to imagine him paying attention over a long period of time,” he said.