Whenever severe winter weather approaches, grocery store aisles are always cleared of eggs, bread and milk.

But why is that the case?

The Centers for Disease Control and Prevention recommends bread as a no-cook food to stock ahead of a storm, but not perishables such as milk and eggs.

A power outage means those foods may not last until the storm passes.

The Atlantic reported that buying perishables may be a matter of psychology.

Duke University behavioral economist Dan Ariely said it’s a matter of seeing others doing something and feeling the need to join in.

“If we go somewhere and we see other people buying those particular things, all of a sudden (we’re) even more interested in those,” he said.

“It’s like saying, ‘The storm will be over soon and I won’t be stuck in this situation for long,’” clinical psychologist Judy Rosenburg told HowStuffWorks.

So it may be fine to get bread, milk and eggs, as long as you have enough non-perishable foods as well.