If you find yourself being pursued by a hungry bear in the woods, label each of these items in your backpack as either 'useful', 'not useful', or 'an unfortunate choice to pack':  a fish, a gun, a book, a hamburger.
In such a situation, being pursued by a hungry bear in the woods, a fish would be 'not useful', a gun would be 'useful', a book would be 'not useful', and a hamburger would be 'an unfortunate choice to pack'.