Wirth's Law states that software efficiency tends to decrease as the complexity of the software increases. This principle highlights that as more features and functionalities are added to a program, the time taken to execute it often increases, leading to slower performance. Essentially, it suggests that adding more code can lead to diminishing returns in terms of efficiency. The law is named after Niklaus Wirth, a Swiss computer scientist known for his work in programming languages and software engineering. Wirth emphasized that software should be designed with simplicity in mind, advocating for a balance between functionality and performance to avoid unnecessary complexity.