You're asking for a logical explanation from a guy who once wrote this:
You would be wise to listen what I have to say, or you will never improve. Asking a rigid question like this is silly. Its like asking when is Axe technology should be researched. The answer is - when food permits. Sometimes you hard in fighting and need to make villagers instead of making Axe. Same with berries. Sometimes you need whole village working on them to keep fed.
Well played man! It seems you are starting to master the trush-strategy to its full extend. Indeed, like you say: everyone knows it's coming, but it's so powerfull in the way you execute it, that only a few can stop it (The likes of Viper, Jordan, __Duck etc).
Please post more ! :D