As I get older, I become less interested in coming across as an infallible DM. If I was flattering myself I would say this is because I have become more secure; if I was being more realistic I might admit that I just give less of a shit than I used to about most things, as is true for all of us once we hit 40.
This means my approach to gaming has become much more relaxed over time. I don't mind "breaking the fourth wall" where required. If I've made a mistake I'll usually own up to it. If I'm not sure what a rule is, I'll often ask the players. If I've forgotten something, I'll have them remind me. We're just playing a game; I'm not the pope.
(This mirrors what I've found after years of working in education. Young teachers, lecturers, assistant professors and so on will spout all manner of convoluted nonsense, and become red-faced and flustered in the process, in order to avoid admitting they don't know the answer to a student's query. Experienced hands are happy to say, "I don't know, but I'll look it up for next time." [If they're really boxing clever, they'll say, "I don't know, and your homework is to go away and see if you can get the answer for next week's class."])
The question of take-backs, though, is one I find tricky. The latest excellent post on Against the Wicked City is about those game-ruining powers of which the PCs can sometimes fall into possession: things like at-will high-speed flight, non-corporeality, mind control, and so on. Is it ever legitimate for a DM to say to the players: "This power you now have is ruining the game by making everything too easy and I should never have made it possible to have it. Let's say that tomorrow you wake up and it mysteriously no longer works"?
This question is somewhat apropos. In my weekly campaign, the PCs have managed to get their hands on a limited form of telepathic communication (complicated because of the involvement of a third party), that almost functions like a radio operable up to infinite distance. Not apparently game-ruinous yet, but one can envisage it having such an effect. I was grateful to the players that they said, as soon as it became obvious that the strange combination of NPC allies and items that had come into their possession suddenly made an infinite walkie-talkie power possible, that they were happy for this power to somehow be revoked if it proved game-ruinous. But what if they hadn't?
I am a big proponent of giving the players agency. But at what point does agency end? At what point does it become legitimate to say, "The demigod of storms has risen in the East and now nobody can fly at will any more"?