That headline comes from warnings issued to Americans during the World Wars of the last century. It was a reminder that sensitive data that was discussed publicly could be overheard by those working for the enemy. Military and diplomatic history is full of tales in which a careless remark doomed a battle or other operation.

The same holds true for the business world. In my ad agency days, I remember working on a hard-fought effort to keep a large client. Several people in the organization’s marketing department disliked my agency’s team and hoped to replace us with another shop that employed their friends. The run-up to the selection involved weeks of late hours and anxiety, because job cuts invariably follow the loss of a large account.

Fortunately, less than a week before our presentation, we gained information that gave us the upper hand. Our opponents in the client’s marketing department had told us to base our recommendations on a specific budget level, and then told the other agencies that the budget was five times that amount.  How did we discover that? One of those marketing wizards had one drink too many at a local watering hole frequented by ad execs (these were the waning days of the “Mad Men” era, and many ad types still gathered for couple stiff ones before heading home). He gleefully told his drinking buddy about how he and the others had hoodwinked us … never realizing that two of our execs were in the next booth transcribing every word he said.

Given the flexibility of several million additional dollars, we immediately changed the entire direction of our presentation. The client’s marketing staff was astounded at the big ideas and powerful concepts they saw (especially the handful of people who looked at each other in confusion, wondering why we’d think that big on such a small budget). Thanks to our opponent’s slight inebriation and lack of discretion on an earlier evening, we kept the account and benefitted from its larger budget.

I’ve seen countless examples of similar indiscretion in the ensuring years. Back when I rode the train to and from work every day, I was stunned at the clearly confidential and sensitive material people would carelessly share with their companions. I remember glancing at a highly confidential market research report for McDonald’s over someone’s shoulder. He made no effort to conceal it. Had I worked with a fast-food competitor, what little I saw would have been extremely valuable.

Today, I see people post things on Facebook and LinkedIn that would lead me to fire them if they were my employees. In the current rush to share absolutely everything with absolutely everyone, it’s important to remember that some information needs to be handled with discretion. Loose lips really did sink ships in the past, and they’ll sink your career today.