This serves best as an illustration that a mediocre performance in national exams is not the end of the world. But, we should be careful not to applaud poor performance, raise it on a pedestal or assume that in general, failures make better entrepreneurs than eggheads based on just a handful of examples; for every C grad that employs 80 people, there are tens of thousands of other C graduates who lay about, jobless, drunk, without prospects, knifing and robbing people in alleys....
To bring this home, if you were a parent with a kid sitting KCSE, would you say something like 'son/daughter, I am happy if you manage a mere C, thats fine', even if you knew he or she can bag an A or a B if they put in effort?

Very well said/written. If your child is an A material, well, motivate them go ahead and score that A. If your other child is a C material, let them know that it doesnt mean they are a failure. They are most likely gifted in another area. Explore that other thing they are good at and follow through so that they score an A in that.