It's easy to laugh at those half-witted civil servants and military men who keep leaving our state secrets on the train. Do they, one wonders, post a big notice on their briefcases saying, "Spies, look in here"? And can't you just visualise the look on their faces as they watch their train disappear up the track and realise what they've done?
For me, no visualising is necessary. And I'm probably the only person in Britain who has any sympathy for the dummkopf who left the combination to HMS Vanguard's nuclear safe on the 8.05 to Chippenham.
In my case, it wasn't top secret documents. But you might well argue that a whole set of student Ucas forms - carefully completed - are the education equivalent.
Today, it couldn't happen in quite the same way, because applying for university is handled online. But it was only a year or two back that many of us still worked with paper versions.
Certainly I remember it as if it were yesterday. I was taking a dozen or so forms home to work on the references that can make the difference between acceptance and rejection for some students. If you are going to craft each one personally, there's never going to be enough time to do it in college.
For the students, filling out each one is a major operation involving hours of consultation, research, visits and agonising over their personal statements. Just reading all the worthy advice on how to do it can take you all weekend. So I knew well enough what precious cargo I had in my bag.
Every day, I travel to and from work by train. Every day, I carry my battered old case along with me - as often as not full of marking. I pride myself on never having lost a student essay, never having left the bag behind. But then we all know how the words "pride" and "fall" can so often end up in tandem.
On the fateful Friday in question, my commuter routine changed. A group of us were going out for a meal, and I had three or four colleagues sitting alongside me on the train. When we arrived at London's Waterloo station, we were deep in conversation. Together we left the train, went down to the Tube and headed for the West End.
As the doors slid shut, I noticed my bag was missing. It's only a minute to the next stop - Embankment - but it felt like an hour. I dashed across to the other platform, jumped on a return train to Waterloo and was back on the concourse only minutes after leaving it.
There are 19 platforms at Waterloo, and I hadn't the faintest idea which one we'd arrived on. I felt like crying. Instead I found an information desk. After an age of fussing and tutting, the answer came back: platform 16.
I charged on to the platform. But where the train had stood, now there was nothing. Never before had a platform looked so empty. The bag - and all my students' hopes and aspirations - were now trundling down the line towards Addlestone.
My weekend was terrible, much of it spent rehearsing the speech I was going to give on Monday, which would begin, "Well class, I have good news and bad news." As the good news would be that they had three days to re- create their applications from scratch, I wasn't much looking forward to delivering it.
Tucked away in the bowels of Waterloo station is the lost property office. With little optimism, I trudged along to it on Monday morning.
"It's a brown leather bag," I told the man behind the counter.
"Modern one, is it, sir?" he asked.
"Think 1947," I replied, "and then go back some."
For five minutes he disappeared. When he came in holding my briefcase, I nearly kissed him.
Now my speech had to be rewritten. "I have some bad news about Ucas," I began. "There will be a slight delay with your references due to a heavy weekend on the domestic front."
"Phew", came back the relieved response. "We thought you were going to say you'd lost them."