If you forget everything and you start this moment anew.
1. You wont need to know anything is behind you. You have rationale. That allows you to actually examine your enviroment. If you're in a lit room and there are shadows, you'll assume.
2. If you forget everything you wont forget EVERYTHING. A baby doesn't know crap but it does know how to scream, it knows that something is wrong when its hungry, it knows something feels wrong when it uses the bathroom. It knows that light is bright.
3. The first thing you think someone would do when they wake up in a place they don't know is look around. So yeah, even if they forget where they are.. kinda pointless to say well they wont know what's around them.