If something didn't happen, how can it be said that it was ever possible?

Example question: Yesterday, was it possible for you to climb on your roof, rub your belly and yell: “I’m the king of the world!” at the top of your voice?

If it didn’t happen, then how could it be said that it was possible? If the idea never came into your head or if you just didn’t feel like it at the time.. then how could it be said that it was at all possible? Aren’t “feeling like it,” and “knowing about it” some (but not even all) of the prerequisites for its occurrence?

Another example question: Could your microwave oven fall from where it is right now? Is it at all “possible?” Or is it impossible?
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All things considered, What exactly are the limits in the realm of possibility?