Haiku work, as we read them, by giving us a moment to look at some thing, some event, and see it more clearly than we have perhaps seen it before. The author had to stop to take note of this object, this event, and to write it down (...) Haiku not only give us moments from the writer's experience, but go on to give us moments of our own. The central act of haiku is letting an object or event touch us, and then sharing it with another. If we are the writer, we share it with the reader. If we read a haiku, we share that moment, or one like it, with the writer.
Being small, haiku lend themselves especially to sharing small, intimate things. By recognizing the intimate things that touch us we come to know and appreciate ourselves and our world more. By sharing these things with others we let them into our lives in a very special, personal way. (6)
So, sharing is important here. Haiku is by nature small because the flash of recognition (enlightenment?) itself is small. Make it longer and it fades into intellectualization, as the reader (and also the writer) has more time to play with the language.
Indeed, language is, in a way, the "big enemy" of direct experience (witness the many spiritual schools which prefer silence over big speeches). As Jacques Derrida wrote, "language is always metaphorical," meaning that it can never immediately and fully represent reality, being always deferred.
The problem, then, is how to share insight without spoiling it with language, the vehicle of deferral and intellectualization. One cannot remain silent forever, and one of the graceful solutions invented by the Japanese was haiku (the Western world had equivalents, of course, with the Imagists as the most famous).
Size is not enough, though. The writer must pay attention not to concentrate too much of his/her own "translation" of reality into the haiku, or else there is not enough space left for the reader's own reaction and understanding. Conversely, the haiku cannot be too dry and impersonal, or else there is so much space for the reader that the reaction and understanding find no place to anchor themselves.
Balance, therefore, is the key.
Not too much, not too little.
The "Middle Way."