Scrum
Here, an overview of the philosophies and theories behind the framework.
Scrum (and perhaps agility in general) is more than a management framework. Some folks might adopt parts of scrum and wonder why their long-term estimations are not any more clear, or wonder why scrum might not be addressing issues outside it's scope.
Scrum is "purposefully incomplete"
Scrum strays from detailed process instructions and instead outlines ways to relate and interact together for a team of folks.
Knowledge Comes From Experience
Knowledge, about a team, about the nature of the work, about the complexity of work, about the completion of work - knowledg of these things comes from our experience.
We will not know about work through intuition.
Our knowledge of the systems we work in is not built-in to our human nature.
Instead, we will know about these things through our observations of ourselves, each other, and the work at hand.
Minimize Waste
Lean thinking is all about maximizing value and minimizing waste. In an org, this could look like refocusing from individual elements or departments or technologies to releasing a wholistic end-to-end value 'stream', no matter how small and incomplete each piece might seem compared to each of it's parts.
Incrementalism is key
Small steps improve predictability. Small releases of value-added elements provide more value than larger long-term complications that have a growing number of 'unknowns' as the project develops.
Transparency, Inspection, and Adaptation
Scrum has a small number of events to inspect the work, adapt to changes, and share clearly what is going on. In order to fully appreciate the details of the events, these 3 themes must be adopted.
Transparency
The details of the work must be seen by all doing the work and all recieving the work. The current reality of the work helps inform the team about progress toward goals.
Inspection
Frequently assessing the work toward shared goals allows quick recognition of problems.
Adaptation
With the work being visible (transparent) and unknowns or problems are revealed (inspection), the team must make changes based on the insights. The team is "expected to adapt the moment it learns anything new through inspection".