"i bought a new guitar, and...

Tell her the same thing when she buys ANOTHER PAIR OF SHOES.

Went with the wife to DSW (Designer Shoe Warehouse) in San Francisco a few years back. She walked up and down the many aisles of shoes stored on shelves like in a warehouse. Finally she picked up a pair of red high heel shoes (Italian brand) marked off 50%, now only $395.00! How she found the most expensive pair of shoes in the store from what must of been thousands of pairs of shoes, I will never know. (No, we didn't buy them, but a women's logic would have been she "saved" money because they were marked 50% down)