The theme for "All Summer in a Day" is bullying and jealousy. Kids, and people alike, can be so mean when they are confronted with someone different than their current understanding or when they are jealous. Margot had known what the sun looked and felt like when she lived on Earth; but, the children of Venus who get to see the sun for two hours once every seven years could not relate to her experience. The children wouldn't have locked Margot in the closet at that very special moment when the sun comes out if it had not have been for William. William is the antagonist who suggests that they lock her up because,
". . .the biggest crime of all was that she had come here only five years ago from Earth, and she remembered the sun and the way the sun was and the sky was when she was four in Ohio. And they, they had been on Venus all their lives, and they had been only two years old when last the sun came out and had long since forgotten the color and heat of it and the way it really was. But Margot remembered."
Here we see that motive behind the rage and jealousy that the children felt for Margot. Whether it is one situation or another, Bradbury brings out a true principle of the human condition with this story; and that is the effects that jealousy can have when acted upon.