Years ago, Native American Indians used to roam the plains of the United States. These Indians would look across the plains, and see all kinds of animals. They would see rabbits running across the field, and eagles soaring in the sky. Now, picture things from the Indian's stand point - he sees the Eagle flying over the Rabbit:
Say to yourself Indian equals Eagle over Rabbit.
Now just use the first letter of each word: I = E over R
However, from the Rabbit's point of view, he sees things a little differently. The Rabbit looks out and sees the Eagle flying over the Indian.
Say to yourself Rabbit equals Eagle over Indian.
Now just use the first letter of each word: R = E over I
Finally, the Eagle up in the sky sees both the Indian and the Rabbit standing on the ground together.
Say to yourself Eagle equals Indian and Rabbit together.
Now just use the first letter of each word: E = IR