There are a number of reasons why people lie. Sometimes it's to spare others pain, sometimes it's to trick them into doing what we want, sometimes it's merely because we're selfish bastards. And sometimes there's no discernible reason for our actions.
The Doctor lies. In fact, he lies a lot. He'll even tell you that. It's one of the few absolute truths that exist within the Doctor Who universe, and "Oxygen" was our regular reminder of this sometimes harsh but necessary lesson.
At the outset of the episode, before our three heroes even leave Earth's oxygen-filled atmosphere for the space station where capitalism is killing workers that have been made to actually pay for the oxygen they need to live and do said work, Nardole (Matt Lucas) tells the Doctor (Peter Capaldi) he wants the truth. About what it honestly doesn't matter, because it's more about the Doctor's reply: "Don't be unreasonable." There are many reasons for the Doctor to keep the truth from his companions — or whomever is in need of his help in any given week — and it's usually because he's working on a plan to save the day, but it's also because, well, he's the Doctor.
The way the story plays out, with the Doctor placing the blame on Nardole's shoulders because he should have known better than to trust him in the first place, is funny to fans, but it also reveals something that we as fans also sometimes forget: The Doctor operates with his own set of rules, and he can change them any time he wants. It's not necessarily that the Doctor sees himself as being better than those with whom he surrounds himself — though sometimes that might be true — but that he's the smartest person in the room and he knows it so we should just let him work.
Sometimes this manifests as lies meant to provoke a response, as it did at the end of the episode. Sometimes it manifests as arrogance. But at the end of the day, the Doctor is still a hero who will do everything in his power to save as many lives as possible. And if a life belongs to someone he really cares about, like Bill (Pearl Mackie), that means even sacrificing his own health and safety for them.
When Bill's helmet and suit malfunctioned as they were about to enter the vacuum of space to escape the other suits, the Doctor gave her his helmet and went without, suffering badly as a result. He became blind, and once Bill awoke and became aware of what the Doctor had done, he lied to her in order to spare her feelings of guilt. In fact, he lied to everyone until the end of the hour, when he revealed to an angry Nardole that he's permanently blind as a result of his actions.
In that regard, Nardole probably has every right to be an annoying wet blanket. We still don't know who is in the mysterious vault that the Doctor is meant to be guarding, but it's clearly someone who's dangerous and who knows the Doctor well enough that they'd be able to smell the metaphoric blood on him. I'm still willing to bet it's the Master (the John Simm version of the Master as opposed to Michelle Gomez's Missy, to be specific) because he fits the bill, but if the Doctor is constantly running off to answer distress calls because he just can't help himself, there may not be an Earth to return to. Or worse, he might not return at all.
Knowing that this is Peter Capaldi's final season in the TARDIS means there's an overwhelming sense of dread that accompanies each of these new episodes. We know the Doctor will regenerate by either season's end or the Christmas special, but that doesn't necessarily mean he's somehow off limits or out of harm's way until then. This episode measured everything in breaths — 40 breaths to get from here to there, 700 breaths until death — and now that the Doctor has sustained an injury of a severity we haven't seen in some time, we're looking at things differently. How many breaths until regeneration begins? How many breaths until we meet Thirteen?
It feels like the ominous ticking clock that's been hanging over our heads since the beginning of the season just lost a few precious minutes as a result of the Doctor's actions. It's hard to fault him for putting his own life on the line to save others for the umpteenth time, but I also selfishly don't want to face the truth that we're quickly approaching the end of Capaldi's run. Maybe if I ask really nicely, Doctor Who could just lie to me for a little while longer.
Doctor Who airs Saturdays at 9/8c on BBC America.