Correction: An earlier version of this article misstated the first name of Polaroid’s founder. It was Edwin Land. This version has been updated.

Walter Isaacson, the man behind the 630-page authorized biography of Apple’s late co-founder Steve Jobs, has been speaking about the emotional process he went through writing the book.

In interviews, Isaacson has said that it was difficult for him not to become too connected to Jobs during the course of writing the book.

“I got very emotionally — more, normally, than you do as a journalist — involved in this,” he told The Daily Show’s Jon Stewart. Isaacson himself said that he got a little caught up in Jobs’s “reality-distortion field” when the late Apple co-founder told the author that he would wait a year to read the book. That comment made Isaacson hopeful that Jobs was not as sick as he appeared to be.

The level of emotion that Jobs showed surprised Isaacson. “He connected emotion to technology,” Isaacson told Stewart. “This is why the outpouring of grief at his death was beyond what most would have expected,” Isaacson says. “I think that emotionalism came from a deep passion for artistic things.”

He repeated that sentiment in comments to the Associated Press.

“Sometimes I’d look up and there would be tears running down his cheek,” Isaacson told the AP’s Barbara Ortutay.

Isaacson was Jobs’s hand-picked biographer, The Washington Post reported, though the former Time and CNN journalist originally balked at the prospect of writing a biography on Jobs so early in his life. Little did he know, he said in the book’s introduction, that Jobs had recently been diagnosed with cancer. At the urging of Jobs’s wife, Laurene Powell, Isaacson started the more than 40 interviews with Jobs that provide the backbone of the book.

In his first interview with Jobs, Isaacson said the Apple co-founder set the thesis for the whole book. In an interview with Charlie Rose, Isaacson said that Jobs “talked about Edwin Land, the founder of Polaroid, and he said ‘Edwin Land once told me that those people who can stand at the intersection of the humanities and science, the liberal arts and technology, that intersection, are the people who can change the world.’”

Initially, Isaacson told Rose, he thought Jobs was being controlling, but he found that this idea of intersection did, in fact, become the central theme of the book.

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