His closest friends, who found the change in him shocking, assumed that Amos had always had his doubts. For instance, on occasion he spoke of a problem experienced by Israeli army officers when they led troops through the desert. He’d experienced the problem himself. In the desert, the human eye had trouble judging shapes and distances. It was difficult to navigate. “That was something that really troubled Amos,” said his friend Avishai Margalit. “In the army you had to navigate a lot. And he was very good at it. But it gave even him trouble. Traveling at night, you’d see a light in the distance: Was it close or far away? The water appeared as if it were a mile or less away—then it would take many hours to walk to it.” The Israeli soldier couldn’t protect his country if he didn’t know the country, but the country was difficult to know. The army gave him maps, but the maps were often useless. A sudden storm could drastically alter the desert landscape; one day the valley was here, the next day it was over there. Leading soldiers in the desert, Amos had become sensitive to the power of optical illusion: An optical illusion could kill. Israeli army commanders in the 1950s and 1960s who became disoriented or lost their way also lost the obedience of their soldiers, as the soldiers understood that there was a short step from being lost to being dead. Amos wondered: If human beings had been shaped so carefully for their environment, why was their perception of that environment still prone to error?
There’d been other signs that Amos was less than wholly satisfied with the worldview of his fellow theorists in decision making. Just a few months before he’d spoken at Danny’s seminar, for instance, he had been called back into the army, on reserve duty, and sent to the Golan Heights. There was no fighting to be done just then. His job was simply to command a unit in the newly acquired territory, gaze down upon Syrian soldiers, and judge from their movements if they were planning to attack. Under his command was Izzy Katznelson, who would go on to become a professor of mathematics at Stanford University. Like Amos, Katznelson had been a boy in Jerusalem during the 1948 war of independence; scenes from that year were seared into his memory. He remembered Jews running into the houses of Arabs who had fled and stealing whatever they could. “I thought, those Arabs are people like me: They didn’t start the war and I didn’t start the war,” he said. He’d followed the noise inside one of the Arab houses and discovered yeshiva boys destroying the Arabs’ grand piano—for the wood. Katznelson and Amos didn’t talk about that; those were events best forgotten.
What they talked about was Amos’s new curiosity about the way people judged the likelihood of uncertain events—for instance, the probability of an attack at that moment by the Syrian army. “We were standing looking at the Syrians,” recalled Katznelson. “He was talking about probabilities, and how do you assign probabilities. He was interested in how, in 1956 [moments before the Sinai campaign], the government had made some estimates that there wouldn’t be a war for five years, and other estimates that there wouldn’t be a war for at least ten years. What Amos was pushing is that probability was not a given. People do not know how to do it properly.”
If, since his return to Israel, there had indeed been a growing pressure along some fault line inside Amos’s mind, the encounter with Danny had triggered the earthquake. Not long afterward, he bumped into Avishai Margalit. “I’m waiting in this corridor,” said Margalit. “And Amos comes to me, agitated, really. He started by dragging me into a room. He said, You won’t believe what happened to me. He tells me that he had given this talk and Danny had said, Brilliant talk, but I don’t believe a word of it. Something was really bothering him, and so I pressed him. He said, ‘It cannot be that judgment does not connect with perception. Thinking is not a separate act.’” The new studies being made about how people’s minds worked when rendering dispassionate judgments had ignored what was known about how the mind worked when it was doing other things. “What happened to Amos was serious,” said Danny. “He had a commitment to a view of the world in which Ward Edwards’s research made sense, and that afternoon he saw the appeal of another worldview in which that research looked silly.”
After the seminar, Amos and Danny had a few lunches together but then headed off in separate directions. That summer Amos left for the United States, and Danny for England, to continue his studies of attention. He had all these ideas about the possible usefulness of his new work on attention. In tank warfare, for instance. In his research, Danny was now taking people and piping one stream of digits into their left ear and another stream of digits into their right ear, and testing how quickly they could switch their attention from one ear to the other, and also how well they blocked their minds to sounds they were meant to be ignoring. “In tank warfare, as in a Western shootout, the speed at which one can decide on a target and act on that decision makes the difference between life and death,” said Danny later. He might use his test to identify which tank commanders could best orient their senses at high speed—who among them might most quickly detect the relevance of a signal, and focus his attention upon it, before he got blown to bits.
* * *
By the fall of 1969 Amos and Danny had both returned to Hebrew University. During their joint waking hours, they could usually be found together. Danny was a morning person, and so anyone who wanted him alone could find him before lunch. Anyone who wanted time with Amos could secure it late at night. In the intervening time, they might be glimpsed disappearing behind the closed door of a seminar room they had commandeered. From the other side of the door you could sometimes hear them hollering at each other, but the most frequent sound to emerge was laughter. Whatever they were talking about, people deduced, must be extremely funny. And yet whatever they were talking about also felt intensely private: Other people were distinctly not invited into their conversation. If you put your ear to the door, you could just make out that the conversation was occurring in both Hebrew and English. They went back and forth—Amos, especially, always switched back to Hebrew when he became emotional.
The students who once wondered why the two brightest stars of Hebrew University kept their distance from each other now wondered how two so radically different personalities could find common ground, much less become soul mates. “It was very difficult to imagine how this chemistry worked,” said Ditsa Kaffrey, a graduate student in psychology who studied with them both. Danny was a Holocaust kid; Amos was a swaggering Sabra—the slang term for a native Israeli. Danny was always sure he was wrong. Amos was always sure he was right. Amos was the life of every party; Danny didn’t go to the parties. Amos was loose and informal; even when he made a stab at informality, Danny felt as if he had descended from some formal place. With Amos you always just picked up where you left off, no matter how long it had been since you last saw him. With Danny there was always a sense you were starting over, even if you had been with him just yesterday. Amos was tone-deaf but would nevertheless sing Hebrew folk songs with great gusto. Danny was the sort of person who might be in possession of a lovely singing voice that he would never discover. Amos was a one-man wrecking ball for illogical arguments; when Danny heard an illogical argument, he asked, What might that be true of? Danny was a pessimist. Amos was not merely an optimist; Amos willed himself to be optimistic, because he had decided pessimism was stupid. When you are a pessimist and the bad thing happens, you live it twice, Amos liked to say. Once when you worry about it, and the second time when it happens. “They were very different people,” said a fellow Hebrew University professor. “Danny was always eager to please. He was irritable and short-tempered, but he wanted to please. Amos couldn’t understand why anyone would be eager to please. He understood courtesy, but eager to please—why??” Danny took everything so seriously; Amos turned much of life into a joke. When Hebrew University put Amos on its committee to evaluate all PhD candidates, Amos was appalled at what passed for a dissertation in the humanities. Instead of raising a formal objection, he merely said, “If this dissertation is good enough for its field, it’s good enough for me. Provided the student can divide fractions!”