Nick Bostrom argues persuasively that much science would be impossible if we treated 'I observe X' as 'someone observes X'. This is basically because in a big world of scientists making measurements, at some point somebody will make most mistaken measurements.

The obvious flaw in this idea is that it's doing half a boolean update - it's ignoring the prior. And scientists spend effort setting themselves up in probabilistic states where their prior is that when they measure a temperature of 15 degrees, it's because the temperature is 15 degrees. Stuff like calibrating the instruments and repeating the measurements are, whether or not they are seen as such, plainly intended to create a chain of AND-ed probability where inaccuracy becomes vanishingly unlikely.