Aside from hygiene, the simple act of hand washing seems to "wipe away" the traces of decisions that leave a person feeling conflicted, said study co-author Spike W. S. Lee, a doctoral student in psychology at the University of Michigan.

After making hard choices, people tend to justify their decisions to make themselves feel better, Lee explained. (Related: "Brain Region for Overcoming Fear, Anxiety Found.")

"You want to feel that you made the right choice, so you justify it by thinking about the positive features" of your decision, he said. This process is called postdecisional dissonance.

But when people in the study washed their hands after making such a choice, they no longer