The edge keeps moving.
When you can't go on that's where you decided to stop. The old internal map has become obsolete and a new, more accurate map is going to take it's place. The time between the old and the new can be a very trying and horrifying time because we don't know what's going to show up and we can't control what's going to show up.
And when you have gone over the edge you will find that there has never been an edge, that it was only an illusion.