Mistake

The Twelfth Doctor told Clara Oswald that he had many many mistakes in the course of his life. (TV: Deep Breath)

Gaspard de Saux-Tavannes apologised to Catherine de Medici after he mistook her for Simon Duval. (TV: The Massacre)

Clara told the Cybermen that killing her would be their biggest mistake. (TV: Death in Heaven)

Astos claimed to have made a rookie mistake. (TV: The Tsuranga Conundrum)