Rather like the SF earthquakes, the surest indicator is the time elapsed since the previous one. But, like the earthquakes, knowing that ones is overdue doesn't make it arrive on time.

Financial crises tend to be cascade failures. One previously-sound institution blowing up takes out another that was owed money from it, and so on. The response of pumping money into the economy like moderator coolant into a failing nuclear reactor works, but makes everyone uncomfortable. And maybe one day the crisis will outrun the pumps.