Enough chitchat for now. Look at the image below and guess which yellow line is longer.
Step 1: Get an Image With Perspective
The source image can be found here on Flickr.
Step 2: Add a Yellow Line
Step 3: Copy the Line
Step 4: Try It Out With Other Images
Step 5: A Simpler View
The effect works because we're tricking our own sense of depth perception. Items that are closer to the horizon are farther away. So naturally if the yellow bar is closer to this it looks bigger even when it's exactly the same length.