How do you decide which business gets your attention on a hard day?

I run more than one business and most days that is not the hard part. The hard part is the day when two things go wrong at once and I only have room in my head for one of them. I used to just pick whichever one was loudest, the phone ringing, the email marked urgent. That is not the same as picking whichever one actually mattered most. Curious how other people running more than one thing at once make that call, gut feeling, revenue at risk, or something else entirely.