Closing Doors Article

I found this really fascinating, I also struggle at times with "keeping doors open"

http://www.nytimes.com/2008/02/26/science/26tier.html?_r=1&ei=5088&en=e1fdede9d5e2a5e0&ex=1361768400&oref=slogin&partner=rssnyt&emc=rss&pagewanted=all