In the Isaac Asimov novel Forward the Foundation, the hero Hari Seldon notices that the politician Laskin Joranum is wearing a wig and appears to have no facial hair at all, not even eyebrows. Hari deduces the reason for this, and spreads it to make the politician appear more unpopular.
How could Hari be so sure? Why didn't he consider the alternate explanation that Joranum has cancer and had radiation therapy and chemotherapy as an attempt to cure the cancer. Cancer therapy is known to often have the effect of losing most facial hair. Similarly, why didn't Joranum attempt to use this as a defense, even if it was a lie? Isaac Asimov is known to be well educated, so he must have known that cancer therapy can have such an effect, and the same is true for Hari Seldon.