What is it about the underdog?

Here I am sitting in front of my big screen HDTV watching the Titans score their first touchdown against the Ravens and I find myself damn near booing the TV...then I realized something, at the beginning of the year when the Titans went 10-0 I was rooting for them. Hell, I wanted them to go all the way that early in the season. Why the sudden change in attitude? I then looked at the schedule for this weekend and realized something, in all the games this week I'm rooting for the underdog. I want Baltimore to topple top seeded Tennessee. I want the lowly Cardinals to pummel Carolina (and ultimately win the Super Bowl). I want Philly to crush New York (well, that's natural as my hatred of Eli Manning is far from a secret), and I want the Bolts to zap the Steelers (again, not too shocking as I don't want any team to get more super bowl rings than the team I root for...and there's a hint as to my team of choice). So, what is it about the underdog that gets me going? I guess it's the love of seeing cages get rattled. But here's the real kicker though...this seems to be a recurring theme with most people out there...everyone wants to see the champs fall. Always. Is it human nature to like to stir up trouble and break the norm or is it American nature? Either way...damn it Baltimore, get it in gear and it's time for me to grab another brew and a fist full of chips.