Reflecting on a decade of XML: Lesson Learned

Hi Folks,

In one sentence, what is the single most important lesson that has been learned from using XML over the last decade?

Here's my take:

   Tasks of greater complexity may be accomplished
   by distilling out and isolating "what is" knowledge
   (in contrast with "how to" knowledge) and 
   expressing "what is" knowledge in a declarative syntax 
   that can be queried, manipulated, and exchanged by 
   machines.

/Roger