In February 2002, Donald Rumsfeld, the then US Secretary of State for Defence, stated at a Defence Department briefing:
There are known knowns; there are things we know we know.
We also know there are known unknowns; that is to say we know there are some things we do not know.
But there are also unknown unknowns ? there are things we do not know we don?t know.
Philosophy, Hieroglyphics, and Technology | Data Driven Investor
Before the discovery of the Rosetta Stone, hieroglyphics were already regarded as information, even if their semantics?
We will explore the knowns and unknowns of our situation.
In the obvious context, you know what type of situation you are dealing with and you know obvious approach to take.
A situation that might fit the obvious domain is reproducing paper airplanes. The paper airplane has been clearly defined; you know everything there is to know about how to create the paper airplane since a child. Now you just have to execute, and the problem is solved.
known unknown ? complicated context
The ?known unknowns? are things you know you need to know but are not yet known. It refers to things we know exist, but we do not have all the information.
An example of a situation in this context is building a software product. There are certainly many ways to solve this problem, but one method is typically better than the other depending on what goal you are wanting to achieve. For instance, if you are wanting to build a product with cloud native architecture, an expert is helpful to shift through the unknowns and create clarity. Once an approach has been identified, you can hire an outsourcing team to build.
unknown unknowns ? complex context
The unknown unknowns are things you didn?t even know you needed to find out. They are unidentified things.
An example of a complex context is an organism or an ecosystem like a rain-forest. Put simply, we know nothing. You don?t know enough to ask the right questions or identify the knowledge gaps.
finally, unknown knowns
Unknown knowns are those moments when you say, I feel like this is the right thing to do. This is a result of years of experience.
Anyone can run with solutions based on known knowns.
In facts, we need to recognize and investigate the known unknowns and of reducing the universe around the unknown unknowns.
 Donald Rumsfeld (February 12, 2002). United States Secretary of Defense.