Here is an illustration:
AAAA AAAA
APAA AABA
AAAA AAAA
AAAA AAAA
Where A is Empty
B is Block
P is Player.
The player cannot move right because one step in the future of his right there is a block. Although in his right currently there is nothing. Since everytime the player moves in space, the player also moves one step in the future in time.