It's a common sense, we all see it every day while shopping, while having a shower, but we don't use it. Our brain compares all the time, so use it for your own advantage as marketers do all the time. Here is a picture of Big Mac I had few days ago. If you embrace every day as a opportunity to learn, you might notice the wonderful design of the box. I don't talk about the "content". First of all,in the front you see your burger, but where exactly? Right in the golden ratio. ( http://en.wikipedia.org/wiki/Golden_ratio ).
Secondly, you can notice the text. It's all upper case and sits right on the burger, which gives makes the burger look bigger. The glass bottle in the back gives the picture depth.
If you prepare your slides, deciding on prices for your new product or you there is a girl interested in you, remember, our brain compares. Simple principle that makes profit.
Sales assistants know it. Professional sales force always first recommend the more expensive product, because from that time any other product price will be compared to the expensive one. Marketers know it, if they want something look big, they put it next to small.
You know it too, pour icy water on your hands and then warm one, it will feel warmer if you didn't cool down your hands first. So remember,
Use comparison to let your message stand out.