Boolean expression will always have the same value.

Code (JavaScript):

1. function Update () {
2.     if (Input.GetKeyDown(KeyCode.LeftArrow)) {
3.         var cam : Transform = Camera.main.transform;
4.         var cameraRelativeRight : Vector3 = cam.TransformDirection (1, 0, 0);
5.         transform.position += cameraRelativeRight * -1;
6.     }
7.     else if (Input.GetKeyDown(KeyCode.RightArrow)) {
8.           cam = Camera.main.transform;
9.         cameraRelativeRight = cam.TransformDirection (1, 0, 0);
10.         transform.position += cameraRelativeRight * 1;      
11.     }
12.     else if (Input.GetKeyDown(KeyCode.DownArrow)) {
13.         cam = Camera.main.transform;
14.         var cameraRelativeForward : Vector3 = cam.TransformDirection (0, 0, 1);
15.         transform.position += cameraRelativeForward * -1;      
16.     }
17.     else if (Input.GetKeyDown(KeyCode.UpArrow)) {
18.         cam = Camera.main.transform;
19.         cameraRelativeForward = cam.TransformDirection (0, 0, 1);
20.         transform.position += cameraRelativeForward * 1;      
21.     }
22.     else if (Input.GetKeyDown(KeyCode.Space) || Time.time - lastFall >= 1) {
23.         transform.position += new Vector3(0, -1, 0);
24.         if (!isValidPosition){
25.             Debug.Log("you F***ed up");
26.             FindObjectOfType(BlockSpawn).BlockSpawn();
27.             // Disable script
28.             enabled = false;
29.         }
30.    
31.         lastFall = Time.time;
32.     }
33. }
34. function isValidPosition () : boolean{
35.     if (transform.position.y < 0.1)
36.         return false;
37.     else if (transform.position.x > 5 )
38.         return false;
39.     else if ( transform.position.x < -5)
40.         return false;
41.     else if (transform.position.z > 5 )
42.         return false;
43.     else if (transform.position.z < -5)
44.         return false;
45.     else
46.         return true;
47. }

The log says that 'function isValidPosition' has always the same value.
I dont know why....

 

You need to call the method properly with
if ( !isValidPosition() ){