Line in the sand

The term line in the sand refers to a point, beyond which a decision made is irreversible.

For example, a company may commit resources to a project. But at some point, a decision must be made to either see the project to its conclusion (or next major decision point) or terminate it; once the decision is made it cannot be undone.

Although there have been several real-life incidents of a "line in the sand" in history, the phrase is best known for an alleged incident in the latter days of the Battle of the Alamo: recognizing that defeat and death were imminent, Colonel William B. Travis purportedly drew a line in the ground with his sword, asking whoever would join him to cross over (according to legend, only one man – Moses Rose – elected not to join the others).