Answer the question about text:

They just dumped me here and left . " This Doctor was different . Charley knew all about regenerations and how they could change him , but this Doctor had sadness written all over his face , a far cry from her Doctor who greeted everyone as if they were old friends , even if they have never met . Something terrible must have happened to him . " The CIA were never the friendliest of people " .

Why does the doctor 's sadness lead the speaker to believe something terrible must have happened to him ?
The speaker has a baseline degree of empathy which indicates to them that the doctor has suffered