Yeah the devs screwed up and forgot to put a hint...My first time through I got lucky and did it fairly quickly but my second time I had to check online. The puzzles in Lunar are difficult, mostly because they're all left without barely any basis on what to do.
I'm not so sure it's a mistake, actually. Game Arts apparently DID include the password on that notice - Prima's unofficial guide for this game appears to be based on a Japanese copy, and in its walkthrough mentions that the note tells you the code (although the guide tells you the code anyway, being what strategy guides do).
Now, it would take no effort to leave the clue in when translating. But the people at Working Designs removed it. And I think I know why. Myght is terribly antisocial. He doesn't WANT visitors. So why would he tell any random John Q. Adventurer how to make it through a puzzle obviously designed to further discourage visitors?
I could be wrong. Even the great minds at Working Designs aren't perfect. But like I said, it is easier to leave something there than to remove something.
And if I am right, then it means: yes, they want you to try trial and error. It's not like they're the first game ever to do that, even with as many options as there are.
And it DOES fit their characterization of Myght to a "T".
"As the good archmage often admonishes me, I ought not to let my mind wander, as it's too small to go off by itself." -Danilo Thann