PART 2: WHAT ROB THINKS...
All right, Part 1 covered the various popular fan theories regarding the somewhat puzzling ending of the Key to Time series. Let's look at the correct one, now.
Sorry! Did I say that out loud? I meant my theory...
THE TYMECIAN THEORY....
Most theories that fandom seem to come up with regarding the end of the quest for the Key to Time perpetuate the idea that the Doctor still ended up doing good even though he appears to be abandoning his mission. I prefer to believe that he didn't. That he was just being irresponsible and decided not to worry anymore about the battle going on between the two Guardians so that he could go back to just travelling and seeing the Universe. We saw him try, already, to take a break from the Quest during Androids of Tara. This does seem to indicate he was getting tired of the whole thing.
This sort of behavior happens in other stories too. In Day of the Moon, he really should have looked into the girl in the astronaut suit more thoroughly but he chooses not to care. At the end of the story, we see him consciously decide to just pursue aimless travel rather than investigate something important. This is just the way the Doctor is, sometimes. He likes to shirk responsibility.
It just so happens that the shirking of his responsibility in Season 16 had some serious consequences. That, because the Doctor never handed the Key to Time to the White Guardian so he could do what needed to be done, the Universe has suffered for it. The Doctor, himself, even realized the graveness of his mistake and tried to fix the problem in a later incarnation. But it was too little too late. Ultimately, he did manage to reduce the negative effects of his failure but he was far from eliminating them entirely.
There's much that happens in the future of the series that supports this idea. But to truly flesh my theory out, I even consult some stuff that went on before the Key to Time saga.
Let's put together a bit of a timeline:
PREDICTIONS AND MISSIONS
Some time ago, the Time Lords received a prediction from the Matrix warning them of the power the Daleks were beginning to amass. Their great prophetic computer showed them a time that would come where the Daleks would challenge the Gallifreyans for their supremacy over Time and easily vanquish them. Horrified at what they saw, the Time Lords knew they had to do something to prevent it.
So they contacted the Doctor and asked him for his help. He was the best candidate to deal with the Dalek Menace. In fact, they were pretty sure that he hated the Daleks enough to wipe them out of existence. If given the opportunity. They had not bargained on his ethics getting in the way so much, however, and he refused to destroy them utterly. But the Doctor had delivered a crippling enough blow to their development by sealing them in a bunker at the dawn of their creation . This slowed down their progress enough that, by the time they emerged from their underground tomb, they had missed several key opportunities that would have caused them to evolve along a different path and made them more powerful (see Part 1 of Dalek History if you want to understand this concept a bit better - http://robtymec.blogspot.ca/2015/06/chronologies-and-timelines-tymecian.html ).
The Time Lords were satisfied with the results. The Matrix was no longer showing a future where the Daleks had taken over the Universe. So the High Council felt they could rest easy, now.
The Guardians, however, were more finely tuned to look into future events. They foresaw a Great War that would erupt between Daleks and Time Lords but the outcome of such a battle seemed unclear. The White Guardian wanted to prevent the whole thing from happening, of course. He saw the incalculable damage the War would cause to the cosmos. The Black Guardian, quite naturally, wanted the exact opposite. He wanted to enhance the effects of the War and plunge all of Time and Space into chaos and oblivion.
Both of them saw that using the Key to Time would enable them to freeze time and make the necessary alterations to achieve their desired outcomes. Both put into effect a plan that would retrieve the six segments so that they could execute the necessary changes. The White Guardian asked the Doctor to find the segments for him. The Black Guardian allied himself with the Shadow and had him just wait at the location of the sixth segment for the Doctor to show up with the other five.
WAS THE BLACK GUARDIAN HOPING TO START THE TIME WARS?
There is a sequence in Armageddon Factor where the Shadow gives the Doctor a vague idea of what the Black Guardian's ultimate plans for the Key to Time are. He explains that the war between Zeos and Atrios was but a staging ground of things to come. That, long term, he and the Black Guardian wanted to create a war in which one half of the Universe was fighting the other.
Is this a description of what the Time Wars could have been? We know that the key combatants were Daleks and Time Lords. But we also know there were other factions involved. Strange beings and races that get described in stories like Stolen Earth or End of Time, Part 2. Was there meant to be even more combatants? We hear General Staal in Sontaran Strategem lamenting over the fact that his race was not able to participate in the Time Wars. I also have a pet theory that the Cybermen from our reality were involved in an early skirmish and may have been, more or less, completely wiped out (this is why the Doctor says "I am getting so old" when he sees the head of a Cybermen in Van Statten's museum during Dalek - it's been a while since the Cybermen have been extinguished from the cosmos). So there seems to be some evidence to suggest that other aggressive races in the Universe were trying to join the battle.
Could it be that the Black Guardian envisioned a Time War where all the races that sought to rule the cosmos were on one side and the rest of the Universe would need to defend itself against them? Was this his ultimate goal?
The White Guardian, on the other hand, wished to arrange circumstances so that the Time Wars just didn't happen at all. Perhaps, when Time was frozen, he would do still more to curtail the development of the Daleks so that they could never grow to a level of power that would make them a real threat to the Time Lords. This way, the Time Wars would never begin.
It's my personal belief that the Time Wars are the great threat to Time and Space that the White Guardian is describing at the beginning of the Ribos Operation. They are also the horrible plan that the Shadow is describing near the end of Armageddon Factor. No one on the production team of Season 16 knew this at the time, of course. The Time Wars weren't even a glimmer in Russell T. Davis' eye, yet. Nor do I think that RTD makes his own connection between the Time Wars and the Key to Time. This is just my own sad personal theory. The sort of nonsense a fan formulates on a sleepless night where he's watched too many episodes and his brain has gone on overload.
A CHANCE AT REDEMPTION
While the Doctor continued on with his adventures, his mischief with the Key to Time starts weighing heavily on him. He may have even stumbled upon shreds of information that indicated that the Time Wars were coming and that his failure to complete his mission for the White Guardian had contributed to their creation. He didn't fully know what the Time Wars would be like. He'd only seen a few scant clues. But he knew he had to do something to make up for his irresponsibility.
It's my opinion that he made these discoveries somewhere after Season 24. In my History of Gallifrey series, I discuss the idea of the TARDIS malfunctioning and sending the Seventh Doctor back to Ancient Gallifrey (http://robtymec.blogspot.ca/2015/10/chronologies-and-timelines-history-of.html). Perhaps those problems with the TARDIS also allowed him slight glimpses into the future that gave him a vague idea of what the Time Wars would be like.
This is part of what prompts the Doctor to become so pro-active when we re-join him and Ace at the beginning of Season 25. He lashes out quite viciously at both the Daleks and the Cybermen over the next little while. Wiping out huge portions of their respective armies. Could it be that he learnt they would be combatants in the Time Wars and was hoping that these powerful strikes against them would reduce their military might enough to prevent them ever being able to challenge the Time Lords? Was it a vague look into the future that helps prompt such a huge change in the Seventh Doctor's personality?
After the events of Remembrance of the Daleks and Silver Nemesis, the Doctor continues operating in such a devious manner against his enemies because he just finds it to be a more effective way of combating evil. But he is pretty sure that he's done enough to prevent the Time Wars. Which is why he does eventually go back to wandering through time and space less purposefully. Particularly after his seventh regeneration.
THE FINAL OUTCOME
Of course, the Seventh Doctor's efforts were not enough. The Time Wars still happen. It's entirely possible that all that survivor's guilt that he experiences throughout his Ninth and Tenth incarnations stems partially from a sense of direct culpability. He had the opportunity to prevent the War way back in his fourth body but, instead, he chose to just screw off. And now he must live with the consequences.
But should he be too mad with himself? Let's remember, if the Black Guardian had gotten his way, the Time Wars would've been far worse. He had planned to get one half of the Universe fighting the other. So denying him the Key to Time, at least, stopped that. More than likely, the efforts the Doctor did make in his seventh incarnation reduced the harmful effects even more. And his decision to become the War Doctor and participate in the battle contained some major damage, too. At the time that he made his decision, many of the Higher Races believed that the Universe would still end up being destroyed as a result of the War. This is why the Sisterhood of Karn wanted him so badly to join in the battle. They knew if anyone could save all of Time and Space - it was the Doctor. He'd done it several times, before.
So, yes, as irresponsible as he was at the end of Armageddon Factor, the Doctor's done a lot to atone for his negligence. And, while a great amount of damage still occurred because he didn't properly complete his mission for the White Guardian, it still could've been a whole lot worse.
In case you missed it, here's Part 1 of the essay...