He was complacent, believing because he’d done the route often enough he’d be safe.
I mean how could he get lost when he said he’d done it before? Because he was so familiar with it his mind wandered and he wasn’t paying attention.
The same thing has happened to me when I’ve been driving the same route home after a long day at work. All of a sudden I ‘wake up’ and realize I don’t remember the drive at all.