10 Most Depressingly Realistic Lessons From Doctor Who

10. Sooner Or Later Everybody Leaves You

This is the only one that has been flatly, directly stated by the show (and by the main character). In the episode School Reunion, The Doctor unambiguously says to Rose what we'd all more or less assumed for a very long time. He lives his life knowing that every single one of the people he knows is going to eventually leave him. Partially (as he points out to Rose) this is just simple math. He's going to live for thousands of years. Rose will probably live to around 80 (less, more likely, as she has a thrill seeking personality and a tendency to not consider the consequences of her actions). What's interesting about this lesson is that we can witness the exact moment he learns it; It happens about 20 minutes into the final episode of The Chase. When Ian and Barbara tell him they want to use the Dalek timeship to go home he flies into a rage. The reason for this outpouring of anger is immediately obvious - it genuinely never occurred to him that Ian and Barbara would choose to leave him given the opportunity. Every single companion leaving scene from that point was met by him with varying degrees of resignation. Only once did he even attempt to stop them from leaving (Tegan) and even that was more about not wanting her to leave hating him than it was stopping her from going. No one in your life is there permanently. That's why having them here now is important. The Doctor learned that in 1965. He's been trying to explain it to us ever since.