Introducing the basic rules of haiku in the early part of this writing, I explained the art of omissions at some length. Perhaps no more explanation may be necessary here.
The Kojien Dictionary defines that 'omission' means to abbreviate and leave out some part in the interest of brevity. Given the definition, what to abbreviate and what to leave out requires a most careful consideration.
Your haiku gains life when you successfully determine key words for expression in 17 syllables. The words that survived your screening convey implied messages. When you have a lot to say, you find it very difficult to say just a little, don't you ?
You can hardly resist saying all you know about your favorite subjectand find it difficult again to omit your favorite words. While you are supposed to grow your knowledge, you need to learn how to give up words so that a haiku may carry only those that cannot be spared.

taiyo no yatto nozoita tsuyu no sora @(Masaaki)
glimpse of the sun showing finally break of rainy season

This was made by a third-grade student at a junior high school.
Apparently he is bored of the gloomy rainy season and eagerly aspires to play in the open air. His youthful joy sparkles at the glimpse of the sun showing finally through a break of the rain.All these emotions are omitted but implied in the word 'finally.'
The following is also a haiku made by a junior high school student.

oshiire ni chiisaku natta natsu boshi (Teiichi)
in the closet grown small summer hat

Children grow surprisingly fast. One day quite a few mothers suddenly find their growing children looking down on them. A little summer hat was casually found in the closet,and a fond sentiment of bygone child-hood|"I used to be a small child"| must have welled up in the heart of Teiichi. But he properly omitted his sentiment, didn't he ?
A haiku which is stuffed too much has little left in there to impress you.
Omission is the soul of haiku. It contains the whole universe in 17 syllables. Wonderful, isn't it ?
Basho left some impressive remarks on the concept of omission: "All said, nothing left." He means that if you leave nothing unsaid, you leave no room for the reader to comprehend unspoken message.