[Patient0]

I think this is too pessimistic. One always gains some information, even from a single event. If you're catching the bus one and shows up literally the minute that you arrive at the bus stop, yes, you may have been very fortunate and in fact the bus runs only once per day, but you really ought to assign a lower probability to that possibility now, given your recent single new piece of information. There are ways to express this quantitatively too - but your own intuition ought to be enough of a guide here.

[mr_mitm]

This is classical Bayesian inference. You update your priors when new information comes in. If something happens that you thought was unlikely, you update your credence about this event.

[Patient0]

yes and perhaps the difficulty of using a frequentist approach on a sample size of 1 is why the parent post thought that you cannot learn anything from a sample size of 1...