Again is a terrifying word.

Thursday afternoon, alerts went out at Virginia Tech that shots had been fired and the individual or individuals responsible were still on the loose. The campus went on lockdown. The updates continued streaming out. Everyone flocked to Twitter and their television sets to find out what was happening. Virginia Tech zoomed up the list of trending topics. A police officer had been shot. Another victim had been found.

“It’s happening again.”

In a strange irony, this was the very day when Virginia Tech officials were in D.C. appealing a $55,000 penalty for the university’s response to a 2007 shooting incident in which 33 were left dead. Then, the alert was delayed. Now, Virginia Tech has a security and alert system that is a model for other universities. This time, the notification was practically instantaneous, four alerts within the span of an hour.

Reports are now emerging that the gunman may have been his own second victim, and everyone’s breathing a sigh of relief. After the first startling event, there were no more threats or suspicious activity. Police presence has been stepped up on campus. Everyone has been told to go back to their lives.

But what happened there this afternoon serves as an uncomfortable reminder that, do what you will, there is no safe, only safer.

They had all the protocols in place. The alerts went out within minutes. But that doesn’t stop the slow uncurling of terror in the pit of your stomach.

Now it’s (presumably) over. People can even complain that the lockdown was an overreaction.

But this fresh tragedy is still rattling.

We live in a world where you can’t say, “Never again.” Once the unthinkable happens, it ceases to be unthinkable. Even the past is no guaranteed protection.

So you accept the possibility, come up with plans, establish a system. But nothing can quite prepare you. To go about your day you have to push “again” out of your mind. You hope you will never get the text, the tweet, the e-mail alert with those three most awful words: “It’s happening again.”

Every tragedy is different, of course. A police officer is dead. But this time the students got the alerts. They were inconvenienced, not endangered.

But it kept coming up at the afternoon’s news conference. Again. Not again. “Tragedy again struck Virginia tech,” officials said. “Our hearts are broken again.” It’s a horrible word.

My thoughts are with Virginia Tech.