Here's why:

* Observations: Scientific theories start with observations of the natural world. We see patterns, notice events, and gather data.

* Experiments: To test our observations, we design and conduct experiments. These experiments are designed to isolate variables and see how changes in one factor affect another.

* Support: If the results of our experiments repeatedly support our initial observations and ideas, we begin to build a strong foundation for a scientific theory.

* Explanation: A scientific theory is a well-substantiated explanation of some aspect of the natural world. It's not just a guess, but a well-supported explanation based on a vast amount of evidence.

Important Note: Scientific theories can be modified or even replaced over time as new evidence is gathered and analyzed. This is a key part of the scientific process!

Here are some examples of scientific theories:

* Theory of Evolution by Natural Selection: Explains how life on Earth has changed over millions of years.

* Theory of Plate Tectonics: Explains the movement of Earth's crust and how continents have drifted apart.

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

Let me know if you have any more questions!