Uncover the rocks

I was recently looking at some small manufacturing plants.

 What struck me was the excessive amount of work-in-progress 'on the floor'.

 WIP is like a sea that covers the rocks that represent poor manufacturing practice.

 As you lower WIP levels, these rocks become evident and you find out what you are doing wrong.

But leave WIP levels high and you never uncover the rocks ... and you lose a lot of money tied up in that 'sea'.