WARNING: DOCTOR WHO SPOILERS EXPLAINING REGENERATION SHENANIGANS
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okay so I was kind of not on board with the concept of bi-regeneration, mainly because of how it seemed like all of the Sad and the Trauma that the Doctor had undergone got kind of handwaved away? i'm all for ncuti's Doctor being sort of a fresh start/jumping on point for new viewers, but i didn't get how that could work if like, literally 40 minutes ago he was David Tennant being a sad wet puppy dog of a man
however, after rewatching it, i've realized what i think happened there, and it goes all the way back to something introduced with the 4th doctor's regeneration that was never explained: the Watcher
^this spooky guy
so, for those that don't know (or haven't seen every episode of a show that is over half a century old), the Fourth Doctor regenerates at the end of a story called Logopolis (he falls off a satellite dish, but that's not important right now). all throughout the episode, this weird figure, The Watcher, stands off in the distance, and even intervenes slightly by saving the Fourth Doctor's companion. there's not much given in the way of an explanation until the Fourth Doctor regenerates, saying "it's the end. but the moment has been prepared for..."
the watcher walks up, and gets absorbed in a super rad 1980's digital effect (never change doctor who), while his companion just gives us the not-super-helpful-for-lore statement "He was the Doctor all the time!"
then, in a crossfade, the Doctor goes from Four to weird-powder-man to Five
canonically, the Watcher is explained as a future version of the doctor that comes about in sort of a weird overlapping thing with the doctor's timeline, it's very wibbly-wobbly timey-wimey.
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SO what does this have to do with biregeneration and satisfying character arcs/moving on from trauma?
Well, remember, Fifteen said this, about Time Lords doing rehab out of order:
so, here's the thing: Fifteen is the Doctor AFTER Fourteen (duh, I know?) But to be clear...Fourteen lives out an entire lifetime with Donna and family, gets to a ripe old age, and then, when his lifetime of healing is over, he gets yeeted back through his own timestream just to zoot himself out of David Tennant's chest.
Remember, his first words to Fourteen (after popping out of his chest) are "So good to see you! So good!", not the RTD classic "what?". He greets himself like he's almost expecting this, he then says "does anyone want to tell me what the hell is going on here?" which only makes sense if he's coming from a different point in his own timestream (remember, when two doctors interact, memory gets really weird, 10 and the War Doctor don't remember the events of Day of the Doctor until they live through them as 11).
SO TO BE CLEAR: Ncuti Gatwa is playing the Doctor AFTER he has spent years healing from his traumas. His Doctor is fine because Fourteen takes the time to rest and work on himself.
tl;dr: I didn't like biregeneration at first because I thought it looked like this:
In actuality, it looks more like this:
