Kevin Rutherford has found an interesting analogy, which suggests that lowering the water level is an excellent way to surface the real constraints in a system (you can see the rocks when they aren't covered with water).
What does it mean? In general, there is too much water in the system. In manufacturing, the water is work-in-process (WIP). With all the WIP, it is very difficult to understand priorities and materials tend to move in the direction of least resistance, rather than toward that of most value. In order to get more valuable work out of the system, cut the work being dumped into the system to find those rocks that get in the way.
What about in human activities?
In Lowering the Water Level Dan Markovitz over at Superfactory draws a sharp analogy between inventory levels in a factory and the time available to a knowledge worker....
Dan exhorts us to lower the water level by restricting the time we have available for knowledge tasks. Not only will this tackle Parkinson’s Law head-on, it will also encourage us to look for more efficient ways to carry out our regular tasks.
I might word this differently, but it has the same effect. What do people naturally do when they have ten things on their plate? They work on one and then get stuck or the project manager from another task demands work get done on their project. So they move to another task without completing the first. Classic multi-tasking. Rather than restrict the time they have to work on the activity, remove the WIP. Reduce the amount of projects in the system, and people will have fewer activities to switch, and the individual activities will tend to get done faster. (The goal, of course, is not to finish the activities but to finish the projects associated with those activities.)