how Just-In-Time systems were adversely affected by outside forces?

Answer 1

Just In Time discovered reality. The world is too unpredictable to experience without some sort of safety backlog. Notice that FedEx no longer crows about guaranteed delivery.

They did have a really good advantage beyond just diminished inventories and supply stocks. When labor goes on strike, the pain is felt immediately and folks don't have to needlessly suffer as long as good faith negotiations are on-going. Strikes that used to take months or even years only take days or maybe a hint of one to get the same effect.

On the company's side, JIT has obvious advantages too. I visited an auto factory when a rail car of car doors was being unloaded. They slapped a bar code on each door and the guide said, "Now the computer knows each door, when it will be installed on each car, and even where that car is going when assembly is done." But when someone pulls the handle for the line to stop because something major is wrong, there is some serious stress on the employee who stops the line. I wouldn't want to work that way.