When you hear once-in-a-hundred-year event, it makes it sound quite rare. One might look around and say (for example, in relation to climate) "why are so many of these happening?"
But it is unsurprising statistically. If you know just a thousand distinct geographic places, about 10 of them would experience such an event each year.
Of course there are other compounding factors. Not all events are one-in-one-hundred; some are one-in-ten, others are one-in-five-hundred, and with increasing scarcity by order of magnitude.
Another compounding factor is that the borders for "geographical areas" are fuzzy. Does a one-in-a-hundred year event that happens in Vermont also qualify as having happened in New Hampshire? Probably depends on the type and the specific measurements and the expectation according to history.
And what about aggregate events? E.g. "It's been five hundred years since we've seen this many tornadoes, which tend to happen once every ten years."
And in the opposite direction of the 100 square-inch plot of ground, there is blurring in the other direction: What do they mean in aggregate if they are fewer than expected at a global scale?
So my original comment was just a simple way of taking the average of all of these competing factors and stating a general truth that's somewhere in the middle. If you have X things that are expected to have 1/Y probabilities, then the probability of you experiencing any of them is not 1/Y, it's more like X/Y. (As in very likely.. that's more than 1 so obviously not mathematically correct.) But we often don't think about rare events this way - as no specific event being probable, but some collection of improbable events being almost certain. We perceive them all as 1/Y. It's just a very local way of thinking.
Of course in practice, it's quite hard to know whether conditions in one location are independent from another, or whether there's some degree of correlation or an underlying causal factor. This is why we have climate scientists.
"highest temperature ever recorded in town X" does not mean much.
"highest temperature recorded in country Y" on the other hand is more significant, especially if the country is large.