One of the key principles of a lean system is Just-In-Time.  This is the principle that says that material an assembly line or assembly cell needs to do its thing should arrive just in time for the line or cell to consume it.
The principle also extends to finished goods, usually in the form of producing to a specific order
rather than producing to a forecast.
Just-in-time was the brainchild of Kiichiro Toyoda.  He was building a new plant for passenger cars before world war 2 and needed to change the production system to conserve cash.  Too much inventory was tied up in storage because they were making pieces in large batches.
To free cashflow for necessary components, they had to limit production of any part to just what was needed that day.  This was a huge deviation from what everyone had been doing their whole lives.  Eiji Toyoda described it as needing to brainwash the workforce to think differently in his book Fifty Years in Motion.  That might be a good description of how we can help leaders and others Let go of bad habits or old thinking.
To make Just-in-time work, the system has to flow smoothly from end to end.  To create that flow, Toyota created work cells where as many steps as possible could be done in one place. 
Next they limited what they made to just what was needed.  That evolved to smaller lot sizes, with the ultimate goal being one at a time – single piece flow. 
They also needed to regulate that flow, so they created signals that told people when to switch to different parts based on demand.  So they created a Pull system using signal cards they called Kanban.
So, in a nutshell, Just-in-time means doing as much as you can in One Place.  Making One Piece at a time.  And Building in response to a pull system that set One Pace for the operation. 
One Place.  One Piece.  One Pace.  It works for cars and car parts.  It works in Software development.  It works in project management.  It’ll work almost everywhere.
Need help to figure it out?  Call me.  Let’s see how much it will save you to switch.
Have a great day and I’ll see you tomorrow.