While reading "Causal Inference" book from Miguel A. Hernán, he starts the book with the example:
Zeus is a patient waiting for a heart transplant. On January 1, he receives a new heart. Five days later, he dies. Imagine that we can somehow know, perhaps by divine revelation, that had Zeus not received a heart transplant on January 1, he would have been alive five days later. Equipped with this information most would agree that the transplant caused Zeus’s death. The heart transplant intervention had a causal effect on Zeus’s five-day survival. Another patient, Hera, also received a heart transplant on January 1. Five days later she was alive. Imagine we can somehow know that, had Hera not received the heart on January 1, she would still have been alive five days later. Hence the transplant did not have a causal effect on Hera’s five-day survival.
But immediately he contradicts the example by saying:
These two vignettes illustrate how humans reason about causal effects: We compare (usually only mentally) the outcome when an action A is taken with the outcome when the action A is withheld.
Why is he saying that we compare taking vs withholding, when he clearly says in the Zeus/Hera example that we do not withheld anything, we take action A (heart surgery) on both? It seems to me a big contradiction in the first paragraphs of the book of two really important authors...