Duty of care

The Doctor claimed he had a duty of care, which extended to Clara Oswald (TV: Under the Lake, The Girl Who Died, Hell Bent) and the Eleven, (AUDIO: Whisper) which he took very seriously. (TV: Under the Lake)

After Clara Oswald explained to the Twelfth Doctor that she had a duty of care as a teacher toward Courtney Woods, one of her students, (TV: Kill the Moon) the Doctor took to telling Clara he had a duty of care toward her, (TV: Under the Lake) which Clara said she never asked for. Nevertheless, as a result, he wanted to keep Clara out of danger, (TV: The Girl Who Died) and felt he "had to say something" when he saw the loss of Danny Pink was leading her to act too much like himself in the face of danger. (TV: Under the Lake)

After Clara died, and the Doctor became trapped in his confession dial, he could have left at any time, but chose to find his own way out, reliving the same events for 4.5 billion years. When Clara later asked him about this, having been extracted from the moment before her death, the Doctor revealed that he had done so because of his duty of care, which he could not let go of even once she was dead. (TV: Hell Bent)