Probabilities go up or down, but there is no magic threshold beyond which they change qualitatively into "knowledge".

Well, at some point the upper bound of consequences for being wrong multiplied by the likelihood that you expect to be wrong is so tiny that it's worth less than the mental overhead of keeping track of the level of certainty. Like, I'm confident enough that physics works (to the level of everyday phenomena), that keeping track of what might happen if I'm wrong about that doesn't add enough value to be worthwhile.