Prophecy
As Daneel observed the two top assassins take a few seconds to comprehend what he was saying while looking at each other with shock, he realized that he might have hit a jackpot.
Daneel's gamble was based on all the clues he had acquired in the Hidden Kill Sect so far.
First, he had been through that crash course and the clue he had obtained there was that there was some objective behind designing the course and making the rule that whoever asked to learn the techniques of the Hidden Kill Sect would be subjected to it if they didn't meet the criteria for entering the sect.
Clearly, whoever had made the rule must have had some hidden agenda behind making it so that those who were talented enough would be able to obtain something that was coveted in the entire continent – an inheritance.
The second clue was regarding the prophecy that the system had stated.