It is easy to say, if he had just used common sense he wouldn’t have lost his Common Access Card (CAC). She should have had the common sense not to leave her thumb drive in the coffee shop. What is common sense? It’s the knowledge and experience we start to develop as soon as we are born. For example, the pot on the stove is hot: don’t touch it; the ice is slippery: walk carefully; the information is sensitive: encrypt and protect it, etc.