It's impossible to know anything for certain; almost everything is probabilistic.
Also I'm not sure how to interpret your criteria because timing matters, I don't think saying 'it gets revealed in the end' is very meaningful.
Anyway, on Polymarket specifically, sure, military strikes are a common one. Seems like a useful signal to go hide in the basement. Outside Polymarket, there were insider trades in 2008 that I'm sure were useful.