* Composition: The crust is primarily composed of silicate minerals, which are strong and rigid at low temperatures and pressures.

* Low Temperature: Compared to the Earth's mantle, the crust is relatively cold. This low temperature makes the minerals in the crust more brittle and less likely to flow.

* High Pressure: The deeper you go into the Earth, the higher the pressure. However, the pressure in the crust is still relatively low compared to the mantle. This low pressure also contributes to the crust's brittleness.

* Stress and Strain: When forces are applied to the crust, such as tectonic plate movement, it can experience stress and strain. If the stress exceeds the strength of the crust, it will break or fracture. This is how earthquakes occur.

Here's an analogy: Imagine a candy bar. At room temperature, it's brittle and breaks easily. If you heat it up, it becomes more pliable and bends instead of breaking. The Earth's crust is similar: cold and brittle at the surface, but behaves more like a fluid deep within the Earth.