I remember standing at a doorway in E1M2, a door that hadn't been open when I first passed through which revealed a secret area - it was clearly a maze, I had no idea it was there until it suddenly was, and beyond the reach of the bright light shining through the doorway I saw flickering passages. I was wandering, and sometimes I would progress, and the connection between the two was not clear. I mean real, genuine fear - the game was dark and spooky and I didn't understand how things worked and that certain parts of levels simply didn't matter 'secret area' did not mean anything to me, and in fact the notion of progressing through a level in a linear way to reach the exit was not really anywhere in my head.