Micah Dubinko at XML.com - Life After Ajax?:
"Working on a crossword puzzle with ink means two things: you find yourself more conservative, (You wait until you are fairly confident before committing to something.) and when you inevitably make a mistake anyway, it gets messy to patch things up.
Software development is the same way. No matter how carefully a developer proceeds, at some point a mistake will happen, and if the erroneous code has gone out the door, you have a messy situation that needs patching. At that point, software can begin to look like a badly scribbled-out crossword."