Newton's first law states "An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force."
Lets say you have a pencil and you hold in by your chest and then let go that pencil stayed at rest until you let go of it and when you let go of it that is when an outside force called gravity was acted on the pencil.
Why can't you move?
Newton's first law of motion also known as inertia.