We've had the motifs of "The Hybrid" and of "Telling Stories". I'm wondering if there is another motif in this series of "Iterations" - that is, repeating things again and again to get a solution.

In The Zygon Inversion, the Doctor tried at least 16 times to get peace, having to wipe minds 15 times before he succeeded.

In Heaven Sent, he had to have rather more than 15 iterations to get what he wanted...

I wonder if there have been any other sequences like this in the current series? And if there is another set of iterations to come in "Hell Bent"?

Of course, I could be completely wrong

It proves he's determined

^Which is of course what the phrase Hell Bent means.