I think we've all had that experiance where you just join an empty server to get a feel for a game.
You basically go through what the main character does, you "capture the flag" a couple times, but there's no fun if no one is on the other team........so pretty soon it feels hollow, and you end up getting distracted by mundane details in the lvl.
Then somebody joins and you wonder who it is, you frag for a bit....then they leave, and it's just you again.
I wouldn't go so far as to say an analogy for certain times in life, but it's an understandable concept, even if you don't know the first thing about TF2. (Or games for that matter, that might be a stretch though)
In-game:
=TB2142=so1idsn@ke1 in 10 people are left handed. If you are as well, add this to your sig