✥ ✥ ✥
The best work gets done in the most efficient way when team members can carry out planned work together without distractions.
On one hand, it’s good to be fed with just-in-time understanding about the work one is about to do. On the other hand, constant interruption brings certain disruption at some cost. Being in “flow” is good, and a disruption that is well-intended in delivering a helpful update may cost the Development Team an amount of time to restore flow, that will never be repaid in increased market value.
Deadlines can have negative effects if mandated together with the work to be completed . But to work with no sense of urgency or knowledge of the time available also leads to underachievement .
Agile says that we should respond to change, but a system that reacts to every small external change can become a system that is out of control. Flexibility may be a business goal, but constancy is an enabler for effective work.
When the date to deliver work is not in the near future, people tend to have less focus and postpone important activities. (Just remember when you had to prepare for a test in high-school, when you would start studying really hard the last day before the exam.) In development this could mean that in the early days you would focus on things that are easy or the most fun and you will not work on the most valuable PBIs. This effect is captured in Parkinson’s law that states that “work expands so as to fill the time available for its completion.” 
Compartmentalize all market-facing product realization work in a timeboxed interval, with participation limited to the Development Team. Part of the work includes collaboration with the Product Owner at scheduled times to work towards a Refined Product Backlog, but on the whole this is otherwise uninterrupted time.
During the Production Episode, the team focuses on the Sprint Goal and strives to achieve its forecast to complete all work on the Sprint Backlog. There is an agreement between the Product Owner and the Development Team that no PBIs may be changed or added during the Production Episode. This ensures that the business leaves the Development Team focused and committed so that there is enough stability to work on what is most important: the Sprint Goal. The Product Owner can change the long-term product direction by reordering the Product Backlog, but changes to the Product Backlog have no effect on the Development Team’s work plan until they process its content at the Sprint Planning event at the beginning of the following Sprint. This motivates the Product Owner to think carefully about what is most valuable to work on and to not waste time and money developing less valuable PBIs.
All but the most disciplined Scrum Teams should disallow their delivery scope to change during the Production Episode (except for continuing to pull from the top of the Product Backlog when finishing early). More advanced teams may find efficient ways to negotiate between the Product Owner and the Development Team, in ways that both still find positive and fair. Frequent changes in scope or interruption by management or the Product Owner can cause the team to lose motivation and can be a sign that the business is not faithful to the Vision.
During Sprint Planning, Developers forecast (not “commit”) the volume of work they feel that they can complete during this Sprint and pull that amount of work into their work plan (Sprint Backlog), so the internal is a “gift from the project” rather than an externally imposed completion constraint. New work may emerge from unforeseen requirements or defects during the Production Episode and the Developers update their Sprint Backlog accordingly. This emergent work tends to remain constant across Sprints and, while taken into account by the Developers during the Sprint, there is no attempt to estimate it or account for it in advance.
The duration of the Production Episode is the length of the Sprint less the time allotted to Sprint Planning, the Sprint Review, and the Sprint Retrospective. Four weeks is the upper bound on the length of a Sprint, and they typically last two weeks.
During the Production Episode, the Developers assess progress and re-plan the Sprint in the Daily Scrum. Every day, the Developers update the Sprint Backlog with a new Developer-Ordered Work Plan optimized to achieve the Sprint Goal. Teams also maintain a discipline of Good Housekeeping.
✥ ✥ ✥
At the end of a successful Production Episode the team reaches the Sprint Goal and realizes a new Product Increment that is ready for the Sprint Review. There may remain Sprint Backlog Items in the Sprint Backlog, but enough of the backlog has been completed to have achieved the Sprint Goal. If the Developers finish early, they pull additional work from the top of the Product Backlog, break the work down into a work plan, and continue with the Sprint. When a Sprint becomes in danger of not delivering the entire Sprint Backlog, the team should resort to the Sprint Goal. The team assesses this risk and responds accordingly every day at the Daily Scrum.
The Product Backlog Items that reach a state of Done during a Sprint become delivery candidates for that Sprint or a subsequent Sprint. The decision of whether something is Done is separated from the decision of shipping to market; the Product Owner decides when to release a PBI to the market. The Scrum Team produces a Product Increment at the end of the Sprint that is most often the key candidate for delivery, but more frequent delivery (e.g. of emergency repairs) is possible: see Responsive Deployment. Making PBIs small enough raises the chances that several of these become deliverable every Sprint.
A failed Sprint is one in which the Scrum Team does not achieve the Sprint Goal. (Some practitioners avoid using the term failed and instead might say “A Sprint that did not achieve the Sprint Goal”). It is possible (but very unlikely) that the team nonetheless emptied the Sprint Backlog. Neither the Scrum Guide  nor any broad practice recognize any distinction in action that follows from failed and non-failed Sprints, but the distinction helps underscore the importance of process improvement as the team discusses the Sprint during the Sprint Retrospective.
The amount of work that a team can complete in a single Sprint is called the team’s velocity. It is a measure of the team’s demonstrated capacity to complete work in a Sprint and is usually a measure of relative (or, sometimes, absolute) work per Sprint. The team establishes its velocity based on averaged recent historical performance; given Yesterday’s Weather, the team’s delivery should be in line with the expectations it sets when creating the Sprint Backlog. Because velocity is a stochastic value, about half of the Sprints will finish all Sprint Backlog Items early (before the Sprint is over) while half will miss the mark. Good teams learn to use Yesterday’s Weather to avoid taking too much into the Sprint, and thereby risking not delivering everything; good disciplines such as described in Teams that Finish Early Accelerate Faster will improve a team’s delivery track record.
 Teresa M. Amabile, William DeJong, and Mark R. Lepper. “Effects of externally imposed deadlines on subsequent intrinsic motivation.” In Journal of Personality and Social Psychology, 34(1), Jul. 1976, pp. 92-98.
 MIT project management simulation study.
 —. Parkinson’s Law. Wikipedia, https://en.wikipedia.org/wiki/Parkinson's_law (accessed 2 November 2017).
 Jeff Sutherland and Ken Schwaber. The Scrum Guide. ScrumGuides.org, http://www.scrumguides.org (accessed 5 January 2017).
Picture from: PresenterMedia.com.