Feeling Small
That are times where you realize the world's actual size. The fact that Malaysia Airlines Flight 370 has gone completely off the map and is still missing is mind-blowing. A plane carrying over 200 people going completely off the sight of all eyes and technology in space is hard to believe.
The feeling of being small can result from so many situations. An employee at a massive corporation may get that feeling everyday at work. You could be standing in the highest row or on the floor of a packed NFL stadium. Exhaustedly driving across the country on a road trip can definitely create appreciation for how long the world is, but I bet biking cross-country would multiple that feeling many times over. The Faces of Facebook only contains about a seventh of the world. Maybe a map of flights around the world may bring those feelings; playing Google Earth may have the same effect. It is estimated that over 108 Billion people have lived on this Earth...
In all those situations, while feeling minuscule, you can embrace being part of something bigger. It can be part of a team, community, human race, or a member of this Earth. There is some much in the world that can be explored and experienced.