Observe that for the programmer, as for the chef, the urgency of the patron may govern the scheduled completion of the task, but it cannot govern the actual completion. An omelette, promised in two minutes, may appear to be progressing nicely. But when it has not set in two minutes, the customer has two choices -- wait or eat it raw. Sofware customers have the same choices.
    The cook has another choice; he can turn up the heat. The result is often an omelette nothing can save -- burned in on part, raw in another.

-- Frederick Brooks