If you're unwilling to earnestly, critically examine/scrutinize your beliefs, and discard them in failing that scrutiny or in light of new information, you are doomed to stagnate as a individual.
An important sentiment in these times of belligerent, entrenched ideologies imho.
That time 12 distilled over 50 years of character development into a single monologue.
Not gonna lie, under the late Chibnal era, I was preparing to consider moments like this to be the grand finale of the show in my head cannon.
Capaldi ended so well, in such a beautiful full circle for the character and show manner, it wouldn't have been a problem.