Annoying events encountered while travelling - Applauding the pilot for landing.

Have you ever been on a flight where on landing everyone starts clapping? If you haven't, we're sure that you will, eventually. For those that have, maybe you can help us understand why people do it, especially if you are one of those individuals. What's the theory behind it? Is it gratitude? Are you thankful that the plane landed and you are safe? Unfortunately I haven't had the opportunity to ask anyone why they are clapping when a plane lands, but the next time it happens I will be compelled to do so. If you feel the need to applaud the pilot for landing a plane, why in the world did you board it in the first place? What were you expecting? Did you not think the plane would land upon reaching the destination? Personally, I don't consider the landing of a plane by a commercial pilot to be applause worthy, but perhaps that's envy on my part as no one claps when I do my job. Then again, I don't applaud cashiers when they give me the correct change or the waiter when they bring me the meal I ordered either. Personally, I think I would be insulted if someone applauded me for doing my job, but I guess that's just me. On second thought, I really should have waited for the plane to land before writing this.