The way I see it, if I walk far enough in a given direction, I'll either arrive to my destination or to a point were it's obvious I'm walking the wrong way (ex: I'm leaving the city and I know I'm in the right city, or I'm facing the river and I know I'm on the right bank, etc..); at which point I just have to turn around and start again. Reiterate enough times and you're bound to arrive eventually.