Excuse #1: But It's On Sale
(Also known as: It's really cheap; it's only $12.99; it's such a great deal.)
Ah, the lure of the deal. Retailers so understand that people want a deal that an entire Groupon-inspired industry has spawned from this, and outlets even create fake markdowns on their price tags. This will require a mind of steel, but you must train yourself to ignore the base price and focus only on the offered price. Your only considerations should be: (1) Whether you really need it, and (2) whether the price fits within your budget. Even big discounts can mean big spending.