Doctor Who: 10 Worst Things That Have Happened To The Doctor At Christmas
2. Regeneration
From the perspective of us fans, regeneration can be looked at as an exciting change that brings a fresh look to our favourite show. It can also be looked at as an absolute nightmare that kills off a great Doctor, but let's try and embrace that positive side.
From the Doctor's perspective though, it doesn't seem like there's a positive side to be found whatsoever. Just look at all the evidence: prior to regenerating, the Doctor often gives a long speech about how much they'll miss their current body, and how much they "don't want to go". In addition, the Tenth Doctor once likened regeneration to dying - and even got all teary-eyed while doing so - and then, there's also the fact that actually getting to a regeneration requires some sort of fatal injury to be inflicted.
Plus, the Doctor has no idea what they'll look like when they emerge from that golden fire - they could become old and frail, or young and reckless. It's a pure gamble. Pre-The Timeless Children, there was also the twelve regeneration limit, which meant that each bodily change sent the Doctor one step closer to a final death.
In short, regeneration is quite a bad thing to happen to the Doctor, and the two times it's happened at Christmas - the Eleventh Doctor in The Time Of The Doctor, and the Twelfth Doctor in Twice Upon A Time - weren't exactly moments of festive cheer for him, or for fans of those particular Doctors.