After the beloved tenure of David Tennant and Matt Smith as Doctors Ten and Eleven, carrying the iconic role of the Time Lord was a tall order, but Peter Capaldi's unexpectedly aged but rockstar of a Doctor was loved almost unanimously.
The unexpected choice of casting Capaldi in Doctor Who was a great one, and his version of the Doctor was full of wisdom, philosophy, and compassion, a legacy that he carried forward from his predecessors. Twelve's brand of sagacity was wrapped in his own special sense of humor and humility, and some of his Doctor Who quotes are worth noting and referring to when times get tough.
Kindness Above Everything
“Never Be Cruel. Never Be Cowardly. Hate Is Always Foolish. Love Is Always Wise. Always Try To Be Nice, But Never Fail To Be Kind.”
Every Doctor has something wonderful to say when they reach the end of their journey. Every Doctor Who speech before the start of regeneration is great, and so was Twelve's. When Twelve met the First Doctor in "Twice Upon A Time," he wrangled with moving on and said these words.
Very succinctly, Twelve enunciated what his entire purpose had been: to eradicate cruelty and hate by fighting monsters, to be brave in the face of fear, but above all he wants someone to retain the innate generosity of their spirit and give it away often.
The Weight Of Moving On
“Sometimes, The Only Choices You Have Are Bad Ones, But You Still Have To Choose.”
The Doctor has always been known to prioritize human (and alien) life before anything else, but the one instance he didn't was in “Mummy on the Orient Express." Unpopular opinion is that Twelve was apathetic, but he was more practical than anything else.
When faced with the supernatural entity killing people on the space train, he had to make the tough choice of letting people fall victim in order to defeat the villain. There are always grey areas in morality, and sometimes one must pick between the lesser evil and move on.
Every Life Is Important
“Human Progress Isn’t Measured By Industry. It’s Measured By The Value You Place On A Life. An Unimportant Life. A Life Without Privilege. The Boy Who Died On The River, That Boy’s Value Is Your Value … That’s What Defines A Species.”
Racism and bigotry were the last traits that the Doctor would tolerate in anybody, so when he saw that Sutcliffe didn't value a little boy's life in “Thin Ice," he made his feelings clear on what he really though about people like him.
No amount of technological advancement or financial prowess is telling of a civilization's advancement than the amount of importance given to the most common man.
Mercy Can Change The World
"I'm Not Sure If Any Of That Matters. Friends. Enemies. So Long As There Is Mercy. Always Mercy."
Some fans may think that the Daleks need to evolve beyond Davros, but the creator definitely gave the Dalek's a little twist by coding mercy into their physiological makeup, after the Twelfth Doctor showed a younger Davros mercy instead of eradicating him in "The Witch's Familiar."
Despite saving several thousand worlds and meeting with villains of all sorts, the Doctor taught everyone to show mercy, even to the cruellest, when they need it the most.
Think Before You Act
“Don’t Be Lasagna.”
By itself, these three words don't spell out any special wisdom, but with context they depict the quirky but fun way that Twelve used to get his point across to his companions, who were pretty intelligent themselves.
In this case, the Doctor asked Clara, in “Into the Dalek” about what happens when lasagna is microwaved with its plastic covering on. The answer to that is that it explodes, which is why the Doctor then asks Clara to not be a reactionary lasagna, but think with a clear head and be rational with her actions.
Friendship And Love Are The Biggest Companions
"I Don't Need An Army, I Never Have. Because I've Got Them. Always Them. Because Love Is Not An Emotion, Love Is A Promise."
The Doctor and Missy/The Master have had a contentious relationship through the show, but when she brings forth hordes of Cybermen in "Deep Breath," Twelve reminds her that he doesn't need any army when he has true friendship.
Twelve was not as openly affectionate as his counterparts, but he had deep love and appreciation for his companions. He knew that their care and friendship could save him where an army couldn't, and a person very seldom needs anything more than faithful companions in their life.
Life Can't Always Be Happy
"Nothing's Sad Until It's Over, & Then Everything Is."
“Hell Bent" was an episode that was etched into fans' memories because of the unfortunate erasure of the Doctor's memories of the vivacious Clara. He does meet her later, but he can't recognize his companion at all.
Twelve's intuition and wisdom is on full display when he says these lines, because life is a series of crests and troughs. It can't always be highs, and the lows hit when good things end, just like Clara and the Doctor's run did.
Trust Your Instincts
"What's Wrong With Scared? Scared Is A Superpower! It's Your Superpower! There Is A Danger In This Room, And Guess What? It's You. Do You Feel It?"
While hunting an unknown entity in "Listen," Twelve and Clara end up in the '90s, next to a frightened and very young Danny Pink who is being harassed by the creature.
The Doctor is unfailingly kind to children, and he convinces Danny that being afraid is not a weakness, but a sign that his instincts are working correctly. Heeding his fear and escaping would save his life, so people should embrace being scared and listen to themselves every now and then.