The plimsoll line is the line painted on a ship's hull that shows how low or high the ship is resting in the water.  It is named after Samuel Plimsoll, a member of the British Parliament, who crusaded against overloading ships in the 1870s in an effort to prevent the persistent loss of ships during storms.  He succeeded in passing a law that required all commercial vessels to have a permanent load line painted on the hull, later named the plimsoll line. The plimsoll line makes it easy to ensure that a ship still has sufficient reserve buoyancy to survive a storm.
 
We all have plimsoll lines too, and many of us fill up past our lines pretty regularly.  We plan for projects and take on work on the assumption that there will be few interruptions to our schedules.  But there is always a "storm".  You get sick, your kid gets sick, your co-worker gets sick, your computer crashes, the printer crashes, an emergency meeting is called, you are sent on fire, your team is sent on fire, the federal government asks for stimulus projects...  Although we may not sink in every storm, our cargo usually gets pretty soggy.  Soggy cargo are e-mails sent without attachments, reports that are cut and pasted with the old names still in them, ill prepared presentations that convey only confusion at meetings, and co-workers that begin to mutiny.
 
We need to get in the habit of respecting our plimsoll lines to stay afloat, and the first step towards that is identifying where it is.  A simple start is to start writing down what you intend to complete each day within your chosen time frame.  How much do you really accomplish on that list, before you start skipping lunch and bringing work home?  Only by knowing when you cross your plimsoll line can you begin to incorporate time management tools that will help you stay below it.