Kindness was a virtue held in very high esteem by the Doctor.
The first seven incarnations of the Doctor once succeeded in distilling "the yoghurt of human kindness" and filled comedy "red noses" with this substance. They were thus able to temporarily "mellow out" the Mekon and several of his associates, forcing them to give to the charity which Dan Dare was promoting. (COMIC: Comic Relief Comic)
The First Doctor thanked Joseph Longfoot for his kindness and diligence. In return for the Doctor's kindness in fixing his finger, Longfoot gave the Doctor clues to the location of Avery's treasure. (TV: The Smugglers)
The Twelfth Doctor reassured Alit that she was just being kind when she showed Bill Potts her reflection. He also told Missy and the Master that he was helping the Mondasians due to it being a kind thing. (TV: The Doctor Falls)
In his pre-regenerative speech where he summed up her duties as the Doctor to his next incarnation, the Twelfth Doctor twice repeated that she must "be kind", emphasising that she must "always try to be nice — but never fail to be kind". (TV: Twice Upon a Time)
According to Edith Thompson, Charley Pollard was the only person who had ever been kind of her. Charley showed this, without even knowing, by simply being the only one in the household to talk to her, and remember her name. When Charley died aboard the R101, Edith was not allowed to mourn her. (AUDIO: The Chimes of Midnight)