Fundamental to any Lean implementation is Just in Time delivery. JIT is driven by pull signals, flowing opposite the direction of product, requesting an upstream. Thus, everything depends on the human reaction to that signal, be it a physical kanban card, an electronic signal, a specified container, or the arrival of a tugger.
And humans want to know; Is the signal reliable? Can I depend on it? Does it tell me, every time, precisely what to do? Does it make my life better?
An answer of "no" or "maybe" or "well, it should" is enough to derail the pull system.
Humans need to trust the signal.
The signals need to be trustworthy.
When a pull system isn't working, it's usually one of these two.
Keep on learning.