Principle 3: Use “pull” system to avoid overproduction.
In Scrum, the product owner is responsible for scheduling work deliverables according to business demands. The team works on these deliverables just-in-time, so there is no wasted work.
The pull system is maybe the most important mindset change you need to make if you want to apply the Toyota Production System or Scrum.
In Scrum the team does not “estimate” how much they can do during a Sprint. In Scrum they declare what they want to do within the ongoing Sprint. They decide this at the end of Sprint Planning Meeting # 1.
The pull system is a shock for most organizations. Most of us are driven by the idea that we do need to know upfront what we can deliver. The most urgent question in all Scrum talks, in all coachings and in all trainings is still: How can we plan and how can we be _sure_ to get what we want.
In some cases this leads to the fact, that Scrum teams shall commit to pre-defined Releaseplans upfront. In this case people do not have the chance to pull the items into the Sprint without pressure, because the release plan tells them what they have to do. Product Owners get confused when I tell them: “No – the development does not commit to an release plan. The development team only commits to the Backlog Items the want to do in a Sprint.
Understanding the idea of pulling the work into the Sprint instead of demanding an amount of work from the team is substantial for Product Owners and development teams. Scrum Delivers, Boris Gloger, Scrum Alliance Website  The Toyota Way, Jeffrey K. Liker