Tisha B'Av is a day of mourning and the most somber day of the year. We sit on the floor and mourn the Bais HaMikdash. Yet we find people who not only don't seem to be too terribly deep in mourning yet even treat the day lightly and even joke around. How can we relate to these people?
Our attitude can be guided by a Mashal from Rav Binyomin Finkel. When a father dies young and you make a Shiva visit you may find distraught parents, a tearful widow, sad siblings, and shell shocked children. Yet while all this is going on inside the somber apartment, outside you may find a young child playing and laughing and having a good time, genuinely enjoying the days off with the whole family around and lots of attention.
Do you say to yourself, "well if he thinks his father's untimely passing is a big joke don't expect me to feel bad for him"? Of course not. This child has lost more than anyone inside crying. And what makes your eyes well up with tears is his childish naivety that doesn't even allow him to understand what he has lost. This child has lost his guiding light, the one who will raise him to be a man. He has lost the one who will provide for all his needs. He has lost his emotional pillar and now belongs to a fragile orphaned home instead of a steady and secure one.
We tend to relate to the Bais HaMikdash as a spiritual treasure and therefore those spiritually inclined take the day far more seriously than others. But the Bais HaMikdash was far more than a place to reach spiritual heights. With the presence of the Shechina down here on earth in the center of Yerushalayim, the world was a different world. The people were strong and beautiful, the produce was something we can't even imagine, even the worst weather was more glorious than any day we can dream of.
The Bais HaMikdash was the place where Heaven met earth. Just like we cannot fathom what Olam Haba is like, we cannot even imagine what life was like in the shadow of Hashem's palace. All the bracha in the world flowed through our Bais HaMikdash, and from there to the rest of the world. This gave Am Yisroel extreme superiority in ever facet of Ruchniyos and Gashmiyos.
The most hardened materialistic heart can relate to this as well. And if he laughs about the loss, and cares more about the measly pleasures he has earned, or focuses his mind planning his upcoming thrills, he is truly a sad case and deserves the pity reserved for a naive orphan.