One of the things lenders do in evaluating the risk of a potential borrower defaulting on a loan is to consider the potential borrower' s credit score. In general, the higher the credit score, the less the risk of default. Yet for mortgage loans, the proportion of defaults is much higher for borrowers with the highest credit scores than for other borrowers.
The statement "Most potential borrowers have credit scores that are neither very low nor very high" most helps to resolve the apparent discrepancy in the statements above.