There is some evil in all of us, Doctor, even you.
A child is not a weapon!
The Doctor + chess
Now Rassilon found the Eye of Harmony, which balances all things, that they may neither flux nor wither nor change their state in any measure. And he caused the Eye to be brought to the world of Gallifrey wherein he sealed this beneficence with the Great Key. Then the people rejoiced. [The Deadly Assassin]
Time’s in flux, changing every second. Your cozy little world can be rewritten like that. Nothing is safe. Remember that. Nothing.