Luck

Fred Hoyle's Black Cloud explains genius in human beings:

"'The infrequency of genius is to be explained in simple probabilities. A child must learn a great deal before it reaches adult life. Processes such as the multiplying of numbers can be learned in a variety of ways. This is to say, the brain can develop in a number of ways, all enabling it to multiply numbers, but not all with by any means the same facility. Those who develop in a favourable way are said to be "good" at arithmetic, while those who develop inefficient ways are said to be "bad" or "slow". Now what decides how a particular person develops? The answer is - chance. And chance accounts for the difference between the genius and the dullard. The genius is one who has been lucky in all his processes of learning. The dullard is the reverse, and the ordinary person is one who has neither been particularly lucky nor particularly unlucky.'"
-Fred Hoyle, The Black Cloud (Harmondsworth, Middlesex, 1965), pp. 206-207.

A human scientist deduces that genius is not only rare but also not hereditary:

"'It also explains why a genius can't pass his faculties to his children. Luck isn't a commodity with a strong inheritance.'" (p. 207)

Here, Hoyle anticipates the plot of a Larry Niven novel. The Puppeteers promote the Birthright Lottery because they believe that luck is inheritable. Teela Brown, descended from four generations of Lottery winners, is demonstrably lucky - or so we think, although this judgment can always be revised in the light of subsequent events. Is it her genes that are lucky?

If the Black Cloud is right that genius is a matter of luck and if the Puppeteers are also right that luck is inheritable, then subsequent generations of teelas must be not only so lucky and safe that Niven cannot write interesting stories about them but also so quick-thinking and intelligent that we would not be able to understand their thought processes.