Complexity can't be eliminated, only relocated within the system.
Definition
Tesler's Law, also known as The Law of Conservation of Complexity, suggests that for every application, there is a certain amount of complexity that cannot be eliminated. Instead, this complexity can only be shifted around to different parts of the system.
Do
Balance complexity between user interface and the system
Shift complexity to the parts of the system accessed by advanced users
Simplify user-facing components as much as possible
Avoid
Attempt to remove all complexity from the system
Make all parts of the system equally complex
Underestimate user ability to handle complexity if it’s presented intuitively
When to apply
Designing a multi-functional application
Creating a complex user workflow
Designing for a diverse user base with various levels of expertise