The Butterfly Effect (noun): The phenomenon whereby a minute localized change in a complex system can have large effects elsewhere.
Think about this. Sometime in the summer of 2009, the Philadelphia Eagles made a very crucial decision, that as small in the grand scheme of things as it may have seemed then, has impacted the roster more than anyone could have ever fathomed back then.
The Philadelphia Eagles decided they wanted to take a flyer on Michael Vick upon his release from prison. The Eagles followed their decision to sign him by actually landing him. As controversial as the move was, no one could have predicted what happened next.
Signing Michael Vick led to the Eagles having three quarterbacks on their team. Someone had to go.
Having no more use to them, the Eagles traded one of those QBs, Donovan McNabb, to Washington for a 2010 2nd round pick (Nate Allen) and a 2011 4th round pick (The Eagles traded this pick to Tampa in exchange for Tampa's 2011 4th rounder (Casey Matthews) and a 2012 4th rounder.)
Then after Kevin Kolb got injured in the first game of the season, Michael Vick came in and never looked back. He took the job away from Kolb, and that allowed Kolb to be expandable.
The Eagles traded Kevin Kolb, another QB no longer of any use to them, to Arizona for a former first round draft pick and Pro Bowl CB Dominique Rodgers-Cromartie and a 2012 2nd round pick.
To summarize, the decision to sign Michael Vick has given the Eagles the following things:
Nate Allen (2nd round pick)
Casey Matthews (4th round pick)
2012 2nd round pick
2012 4th round pick.
All of those guys are penciled in to be starters on this year's team, with the exception of Casey Matthews, who may yet win a starting job in training camp.
That, ladies and gentlemen, is The Butterfly Effect.