Here's why:

* Inertia is the tendency of an object to resist changes in its motion. A more massive object has more inertia, meaning it takes more force to get it moving or to stop it once it's in motion.

* Speed is a measure of how fast an object is moving. It doesn't directly affect the object's resistance to changes in motion.

Think of it this way:

Imagine pushing a small car and then pushing a large truck. Both are at rest initially. The truck is much harder to get moving even though both are at the same speed (zero). This is because the truck has more mass and therefore more inertia.

In summary:

* Mass: The greater the mass, the greater the inertia.

* Speed: Speed does not affect inertia.

Let me know if you have any other questions!