Here's why:

* Metals are good conductors of electricity. This is due to their unique atomic structure. Metals have free electrons that can easily move throughout their structure, allowing for the flow of electrical current.

* Insulators are poor conductors of electricity. They have tightly bound electrons that cannot easily move, hindering the flow of current.

Therefore, the properties that make a substance a metal (free electrons) are fundamentally opposed to the properties that make a substance an insulator (tightly bound electrons).

Some materials that are often thought of as "metals" can be poor conductors, but they aren't technically metals. Examples include:

* Alloys: Combinations of metals with other elements can sometimes have lower conductivity.

* Metal oxides: Compounds of metals and oxygen can be insulators.

Let me know if you'd like to learn more about metals, insulators, or conductivity!