What causes an object to fly away on the z-axis by -10?

Question

Unity

Mortire.transform.position = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y , 0));

If you use this

float mouseY = Input.GetAxis("Mouse Y");
float mouseX = Input.GetAxis("Mouse X");

That micro movement with the mouse and my object already begins to pass the 4th dimension

Answer 1

Vector3 mousePosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 10f);
Vector3 objPosition = Camera.main.ScreenToWorldPoint(mousePosition);
Mortire.gameObject.transform.position = objPosition;

Answer 2

Just try

Mortire.transform.position = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y , 0));
Mortire.transform.position.z=0;

Or does it not work like that?