Generally I didn’t have a whole lot of problems with Clara’s sacrifice in NOTD — I would have preferred if it felt less time-loopy/predetermined, but that’s par for the course these days. And I think you can argue that the relationship between Clara and the Doctor felt a little underdeveloped, to the point that it’s potentially unbelievable she would go to such lengths to save him.
And that’s where I think they could’ve salvaged a bit more and didn’t. Clara wasn’t just saving the Doctor — she was saving the universe, as evidenced by the stars blinking out and Jenny and Strax and who knows how many others evaporating while the GI went haywire in the Doctor’s timeline (for whatever misguided villainous reason). Clara saving the Doctor from the GI restores all those planets and people and events, too.
But the emphasis always seems to be placed on saving the Doctor, “I was born to save the Doctor”, which is really underselling what Clara actually did, which was sacrificing herself for the Doctor and the rest of the universe. I think her decision would have been more powerful if they had put more emphasis on that.
Have you ever been in love? Horrible isn’t it? It makes you so vulnerable. It opens your chest and it opens up your heart and it means that someone can get inside you and mess you up. You build up all these defenses, you build up a whole suit of armor, so that nothing can hurt you, then one stupid person, no different from any other stupid person, wanders into your stupid life…You give them a piece of you. They didn’t ask for it. They did something dumb one day, like kiss you or smile at you, and then your life isn’t your own anymore. Love takes hostages. It gets inside you. It eats you out and leaves you crying in the darkness, so simple a phrase like ‘maybe we should be just friends’ turns into a glass splinter working its way into your heart. It hurts. Not just in the imagination. Not just in the mind. It’s a soul-hurt, a real gets-inside-you-and-rips-you-apart pain. I hate love.