Everything is a probability.

When I say Event X is going to happen, I of course don’t know this with 100% probability.

When you say “No, Event Y is going to happen.”, you do not know this with 100% probability, even if you think you do.

If Event Y happens, the fact that it happened says little about your “rightness” at the time of your prediction.  If I think Event X has a 75% chance of happening and Event Y has a 25% chance of happening, but Event Y is what actually ends up happening, that doesn’t mean my estimates at the time were wrong.

This is why “I told you so” is stupid.  It doesn’t increase your stature as an accurate predictor.  The only things that should increase your stature as an accurate predictor is a history of predictions that match with events that happen.  For bonus points your predictions calibrated probabilities should match the real events.

As an aside, the problems related to this include our societies reliance on ‘pundits’.  There is no central clearinghouse for recording well-defined predictions which matches those with their results.  Such a mechanism would help us better pick our leaders and those who advise our leaders.