There are two wines for sale at dinner: $9 a bottle or $16 a bottle. Which one do you order?
Now, imagine that there are three, and the third is $34. Are you more likely to buy the $16 bottle now? Most people are.
Competition is almost always a good thing, and marketers can create it... or highlight it. More here: The Decoy Effect, or How to Win an Election - washingtonpost.com.