Father and son heights are an example of regression to the mean in this book. Above average height father will tend to have a son who is shorter, while still above average.

Conversely, an above average height son will tend to have a father who is also above average, but shorter.

While this seems like a contradiction, these are tendencies across an entire population that will always trend toward the mean height.

This reversability of prediction in regression to the mean is why there is no difference between cause and effect in this situaton.