When it comes to statistical measurements, the standard accepted error margin for a new result to be considered a legitimate discovery is very small, but it's still possible for the result to be outside that range by sheer chance.

For example, imagine an experiment that examined cancer rates in connection to smoking said that there was only a 1 in 1 million chance that smoking did not increase chances of getting cancer, and all seeming connections were just a coincidence. That's a very, very low chance of it being unrelated, but it's still possible, and 1 in a million chances happen every day.

If a second experiment is done, using an unrelated dataset, and it also finds the same thing at the same chances, it greatly reduces the chance of the first dataset supporting that conclusion by sheer fluke. It's still not completely impossible, but the chances of both experiments being flukes is exponentially lower than just one of them being one.