Indeed, this type of "surprises" is how you know you are probably on the right track with your choice of abstraction. But I still find the word "surprise" reasonable for the emotion I feel when I observe something like that. Very pleasing reassuring intellectually satisfying surprise. A "sufficiently smart armchair theorist" might discover these "surprises" in advance simply from consistency and beauty and simplicity considerations, but these armchair theorists are usually just a made up thing we imagine when teaching.

I corrected the wrong use of the word associative, thanks!