Every student under Landau was tableware among tragedies, because Landau's IQ was simply too high and his students could not understand what he taught. During class, Landau simply hung a painting on the blackboard: a shepherd playing a flute, with a flock of little sheep grazing beside him. The students racked their brains but could not make sense of it, so they could only risk being scolded and ask Landau about it. In fact, Landau's meaning was summed up in four words: "playing the lute to a cow."
After Landau realized that his students could not understand what he was saying, he raised the threshold for becoming his student to a downright insane level. If you were born in the Soviet Union and had heard that Landau's graduate program was extraordinarily difficult to enter, and wanted to challenge yourself, then first, you needed mathematics; second, physics; and third, still mathematics.
Every student under Landau had to prepare a thick notebook and complete several thousand problems. In the end, Landau would personally set the questions, covering every aspect of theoretical physics. The mathematics alone was enough to send people fleeing in defeat. A student seeing the exam paper for the first time might feel like this: Why is it so thick? Bang head against wall—Why am I not allowed to look things up? Bang head against wall again—Why are the physics concepts so difficult? Bang head against wall—The math problems cannot be solved. Might as well die.
In the entire Soviet generation, only a little over forty people successfully cleared the hurdles. Later, every one of them became a backbone of Soviet theoretical physics.
Landau's thinking was probably this: Since there was nothing to be done about their low IQs, he could only help them build a solid foundation. It was just that the "foundation" by his standards was rather different from everyone else's.