Have you ever had to listen to your parents talking about the way things were when they were young? Besides the walking to school uphill both ways -- barefoot in the snow, no less -- they probably reminisce about when a McDonald's hamburger cost $0.15, or gas cost $0.25 a gallon.

"These prices today," they snort, "they're just insane." "Four dollars for gas? Eight-nine cents for a hamburger? Scandalous!"

Never mind that a gallon of gas in 1918 cost $3.50 in today's prices, or that that 1955 hamburger cost $1.21. Yet 15-cent hamburgers and gas for a quarter are the standards by which all other prices are measured.

And you do the same thing.

Don't listen to your gut
According to a study by MIT behavioral economist Dan Ariely, the first price we encounter for a given item shapes how we view every price we encounter after that.

He asked a group of MIT MBAs to write the last two digits of their Social Security number -- in dollar terms -- next to each of several listed products and then indicate whether they would pay that much for each items. Then he asked them to write down the maximum amount they would pay for each product.

The students with the highest ending Social Security numbers bid the most, while students with the lowest ending numbers bid the least. In other words, the price we encounter first for a given product becomes an anchor -- and it, rather than any underlying value, provides our gut sense of whether something is cheap or overpriced.

Noted financial journalist Jason Zweig found the same thing when he looked into neuroeconomics to explain why smart people make bad decisions about money:

As soon as your intuition seizes on a number -- any number -- it becomes stuck, as if it had been coated in glue. That's why real estate agents will usually show you the most expensive house on the market first, so the others will seem cheap by comparison -- and why mutual fund companies nearly always launch new funds at $10.00 per share, enticing new investors with a "cheap" price at the beginning.