Every item we buy has a huge markup on them due in part to the many business processes it goes through and on the supply/demand. A pair of shoes, which cost 10$ to make, will sell for $100 by the time it reach the consumer.
When items go on sale, they are a bit cheaper to you but not cheap enough to make the seller cry about it.
"If you don't master money, it's going to master you." -Tony Robbins
Sales are just attempts to make more money out of us. It plays with our "If I don't buy it, I'll miss out" feeling. We shouldn't buy items that we don't need simply because it's on sale.