Why are adults so much more vulnerable to the sunk-cost bias than young children? The answer, he believes, is a lifetime of exposure to the “Don’t waste” rule, so that by the time we are adults we are trained to avoid appearing wasteful, even to ourselves.8 “Abandoning a project that you’ve invested a lot in feels like you’ve wasted everything, and waste is something we’re told to avoid,” Arkes said.9.