The harder you try, the worse you fail

I just read an interesting article about over-spending while you're in the store. Basically, the more closely you try to estimate your spending, the more you'll over-spend.

There's absolutely nothing wrong with taking a calculator with you to the store, but if you're caught without one, estimate by rounding to the nearest whole dollar.

The article I was reading is summed up nicely at http://www.mindlesseating.org/tryingharder/