Okay--I got it. "Line in the sand."

Why, why, why do people use this expression? Have I missed something, somewhere that would help me understand it. A line in the sand shifts with the wind and the water and small children scooping up parts of it for sand castles. A line in the sand cannot be a definitive demarcation.

I'm pretty sure I heard this cliche used before moving to West TN, but I never really noticed it before. People here use it all the time. I've heard it twice today.

The legend goes that at the Battle of the Alamo, what's-his-face took a "if you're not with me, you're against me" approach, and urged the With-Mes to step over a line he drew in the sand. Once they joined him, there was no going back, and there was no chance for anyone else to cross the line. In this case, it works. General What's-His-Name created an irrevocable assignation, only signified by the line in the sand, which is prevalent around the Alamo.

Perhaps I am unveiling my cynicism here, but everyone who has uttered those words--from confessing criminals to politicians--rarely lives a life that reflects their "line in the sand." So...I can't help but take away from the expression that it is a statement, indicative of a stance that changes based on the weather, the passersby, and erosion.