My new favorite expression is "It's like nailing jelly to a wall". I find it to be a very useful expression in software development and IT, especially in the write anything, for anyone, at anytime, for any price world of mobile enterprise application development.
I've found a valuable scientific resource which probes this very important topic:
"We've all heard the old saying "it's like nailing jelly to a wall" to describe a task that is very difficult or impossible. But is our view of the difficulty of this task justified? Has anybody actually tried nailing jelly to a wall? In this experiment I attempt to establish, one way or the other, the validity of the old proverb."
http://graeme.woaf.net/otherbits/jelly.html