How to make wise spending choices

Why do so many otherwise rational individuals make irrational decisions when it comes to money? Why do shoppers overspend when using credit cards, but manage to stay in a budget when they use cash? And why would a person walk five blocks to save $10 on a $20 purchase, but not on a $1,000 suit?

“Our brains evolved to make decisions on the savannah or in a jungle. And a lot of the decisions we have to make as adults in a modern world aren’t necessarily applicable to what we might have made 10,000 years ago. The decisions aren’t crazy; they are simply obsolete.”
–Gary Belsky on irrational spending behaviors