Because it is during those periods when you need your friends the most and when it is most inconvenient/difficult for fake friends to come to your aid. It is naturally the most effective way to separate the wheat from the chaff, even though it may not be a nice process.

It's easier to demonstrate a counterfactual than to prove the theorem. Therefore the burden of proof should be on you to demonstrate the counterfactual.

I don't think you're wrong, I'm just asking for some elaboration.