Final answer:
No, something cannot have so much inertia that it cannot be moved. Inertia is proportional to mass, and while massive objects require significant forces to move, they are not immovable. Forces like gravity can change the motion of any object, no matter its mass.
Step-by-step explanation:
According to Newton's first law, often called the law of inertia, a body will remain at rest or in motion with a constant velocity unless acted upon by a force. The reason why something could never realistically have so much inertia that it can't be moved is due to the fact that inertia is a property that is proportional to mass. While large objects like Earth have enormous inertia and require tremendous forces to alter their movement, in practice, forces such as gravity or even human-made ones can and do cause such objects to move or change their velocity.
For example, when a football player runs into a goalpost, both the player and the Earth experience forces but because the Earth is so massive, its motion in reaction is imperceptible. However, we can't say the Earth is immovable; forces exerted by other celestial bodies cause it to move, proving that no matter how large an object is, as long as it has mass, it can be moved.
This notion is further corroborated by the fact that even in outer space, where friction is negligible, objects still can move or coast indefinitely. This demonstrates that inertia doesn't make an object 'unmoveable'; it just describes resistance to changes in motion.