Here's why:

* Well-tested concept: Theories are not just guesses; they are supported by a large body of evidence and have been rigorously tested through experimentation and observation.

* Explains a wide range of observations: Theories provide a framework for understanding a broad range of phenomena, often unifying seemingly disparate observations under a single, cohesive explanation.

Examples of theories:

* Theory of evolution by natural selection: Explains the diversity of life on Earth and how species change over time.

* Theory of relativity: Explains the relationship between space, time, gravity, and the universe.

* Germ theory of disease: Explains how microorganisms cause illness.

It's important to note that while theories are well-supported, they are still subject to revision and refinement as new evidence emerges. However, the core principles of a well-established theory are unlikely to be completely overturned.