Considering how bad many people are at managing their finances(USA credit card debt, I'm looking at you), it's no wonder people buy groceries that end up in the waste bin.
Distinguishing needs from wants
and
Estimating how much of something is necessary to fulfill a need.
The recipe for a cake I made recently calls for 14 oz of maple syrup. I can buy it only in 12.7 oz bottles.
Distinguishing needs from wants
and
Estimating how much of something is necessary to fulfill a need.