I looked up what is required in the excellent guide by pecan, but I don't understand how I'm meant to have figured that out for myself.

Even after mapping out the relationships between the letter sets, with no hints or guidance it just seems like too daunting a task to figure out what kinds of words its looking for. I feel like I've missed a note or something.

It's rather frustrating, especially as solving the puzzle seems to be a requirement to finish the game.