“Rule of six” - what else could it mean”

[Stannisbaratheonsboxofmatches]

It puts me in mind of a sci fi or fantasy adventure book -“The Book of Six” by Boris R R R R Johnson.

What does it put you in mind of?

It reminds me of the 'bad things happen in threes' motto my mother lived by. I'm sure we're well beyond 'the rule of six where Johnston and his government are concerned though.