Zen brings with it a trans-interpretative background which seems to be beyond our human ability to bring it down into our world thus to make it, specifically, intelligible for us. This background, especially, is present with regard to Zen's koans. It can also be imagined as a kind of ontological background—though not metaphysical or abstract—where the koan is answered. Such a background is never apparent to human beings in their practical day-to-day life even though koans, for example, appear to be speaking from the ordinary life. This always leads to tension between our ideas of ordinary life and Zen, proper, which is far from ordinary.
In more detail, on one side is our practical day-to-day world together with our personal life and contrasting this, Zen's mysterious trans-interpretative background that seems to haunt every koan; a seeming kind of nonsense but very important. It is not just nonsense in the ordinary sense that every koan brings with it but a special kind of nonsense, which acts like a barrier that can only be dissolved if we directly access the trans-interpretative background which is symbolized by Mumon's no-gate. At this point the nonsense/barrier is no more.
The most perplexing part of Zen for any Westerner is in trying to force Zen to be intelligible in Western terms, notions and contexts. It ain't going to happen—I can tell you that. If the adept still insists on trying to make Zen intelligible in a Western sense it will only lead to a kind of exhaustion of one's enthusiasm for Zen and eventual disheartenment. This then becomes a problem of wishful thinking, tied to a will that refuses to recognize its limits; which I see has a major stumbling block for those new to Zen.