system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] What’s stopping the Ninth Doctor from bumping into a Time Lord from BEFORE the Time War in their time stream (like an early incarnation of The Master)

We know from Big Finish and the comics that the Doctor and Master meet out of order (Five and the Alex MacQueen Master & Twelve and the Delgado Master).

So what’s stopping the Ninth, Tenth or Eleventh Doctor from bumping into an early Master, or Romana or the Monk etc.?
gpt
I mean, nothing in particular. But also, space-time is really big.

There's nothing *stopping* them from bumping into an early master, but it's perfectly reasonable that that the two simply haven't crossed paths. It's like walking around a city and not bumping into anyone you know, except the city is the entire universe from the moment of its conception to its end.