I am particularly struck by those of you who point out that this koan is considered to be especially hard.

Yes, you're right, but I don't think you're appreciating what aspect of its interpretation is supposed to be difficult. The pattern that is being communicated is easy to understand. The challenge is determining what that pattern is meant to be applied to.

There are two relatively simple interpretations of that pattern, and one that is much less so. But that final interpretation is much harder for Zen students to perceive than for people who aren't. In fact, if you've grown up in a Western, English-speaking culture, I can virtually guarantee that you've been exposed to the third possible interpretation many times from multiple sources and in many different ways.