"All journeys have secret destinations of which the traveler is unaware" - Martin Buber
Japan is an intricately organized society burdened with paperwork but maintained with policies, rules, and red tape. Part of the nation's success is due to its citizens seeing their jobs as more than a paycheck. Biologically speaking, everyone has two parents, a mother and a father. But in Japan, there exists a third, the company you work for.
In the case of teachers, it's very difficult to get away, and very few teachers even come close to using half of their paid vacation leave. Though with the existence of several large travel agencies, such as JTB or HIS, someone is hopping on those planes. But who?
The answer: everyone. When I first aquainted myself with the Japanese workplace, I was dumbfounded when many colleagues had confessed to never leaving the country, let alone a trip to the southern islands of Okinawa. It was only after befriending them did I realize that everyone was lying. While, Japanese people are portrayed as shy, and speak less English than neighboring Asian countries, they love exploring the world, if only for a few days at a time.
Then why do they, especially teachers, work so hard to keep their travel on the downlow? It's simple: they're lazy and want to be left alone, but you can't blame them. As a teacher in Florida, all I had to do was input my requested days on the computer and my vacation time was automatically approved. In Japan, not only does your Vice Principal and Principal have to sign off, but if you're traveling, you need to submit a detailed travel report.
Just like a child going on a camping trip with friends, educated adult employees need to supply precise dates, locations, hotel addresses, phone numbers, and emergency contact information. Perhaps, the true reason for keeping the trip secret deals with the return. For any employee missing work is expected to 'thank their co-workers for picking up the slack while they were gone.' This is done with おみやげ / souvenirs, typically of the edible kind. For the first two years, I loved picking up boxes of cakes from exotic countries for the staff room, and personalized presents for my favorite co-workers. But now in my third year, I've grown tired of the ordeal. With bag limitations, and strict travel budgets, it's sometimes difficult to supply the necessary 'thanks.' This is why one co-worker didn't publicize his relative's wedding in another prefecture, and why another secretly took his family to Europe during winter vacation. It also explains why I need to keep my mouth shut. For instance, I only told two colleagues that I was traveling to China, and then everytime I was at the photocopier, someone would approach me and say, "China!"
Consequently, I can't blame any of my co-workers for not telling anyone about their trips, well except me.