[mutatio]

I could see the opposite of that possibly arising, e.g. doing something irrational like creating a training event every 2 decades, due to belief - but the inverse makes no sense to me, what's the advantage to a society to renewing skills at 20 year cliff-edges vs. continual development? Makes less sense still in the context of Japanese kingdoms, the kingdom choosing to continually propagate skills would win.

[beaconstudios]

Because skills aren't always generalisable. For the Ido shine, for example, there's a specific building skillset they use for building temples. New temples aren't built often enough to keep those skills sharp.

> training

Training doesn't impart skills unless the theoretical knowledge is actually used. What better way to use it than to build a temple?