Outstanding is an ambiguous word. Something that stands out is different from the rest. An outstanding result is an extraordinary one, and the word is specifically positive; on its own it implies excellence. But something that is a matter that still has to be dealt with or a debt that has not been paid is also said to be outstanding.
A similar word is overlook. A hotel room can overlook the sea or you can overlook (i.e. ignore) a mistake that someone has made. The basic meaning is the same but in one case by looking out the sea you can see it from above while on the other by figuratively looking over a mistake at something else you do not see what is below you.