What are your thoughts on "Just write."?

The simple advice "Just write." is dished out plentifully in writing discussion boards (especially those frequented by many aspiring writers).

Although it can be hard to hear for a beginner, I believe it's worth internalizing. It is relatively easy to come up with excuses for not writing. What's hard is writing despite it all. Being able to do so is invaluable.

What are your thoughts on this mantra? Criticisms? Perspectives? Stories? I'd like to know.