The reason would be, that you can see that the sky is rotating around a certain point in the north, or south depending where you are. All the stars are changing - but this point is not. So even when there is no bright star at that spot - there will be star constellations around pointing towards it. A fixed point or area of reference ( and with no artificial lights, there definitely would be some star to see).

But of course if you really know the dark sky well, there are a lot more points of references, you will remember what constellations will be where at what time of the night at what season. Or where the moon is, etc.