i've noticed that too...at first i thought it was watched pot syndrome, where it just felt like they got less done, but i've noticed that my village actually gamed everything faster when it was smaller and I didn't keep the app open, than when it got larger and I would occassionally forget to close the app and just minimize it.
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Why is it that if someone tells you that there are 1 billion stars in the universe you will believe them,
but if they tell you a wall has wet paint you will have to touch it to be sure?