This Mark Twain quote is one of my favorites as an English teacher:

I didn’t have time to write a short letter, so I wrote a long one instead.  
— Mark Twain

The phrasing is counterintuitive: we are inclined to think longer equals more time. But that's where the true insight of the quotation lies. Writing is deceptive in its simplicity, and anything but linear.  Being concise requires more effort in the form of editing and organizing thoughts than simply pouring your thoughts out onto the page.