Alright, lets simplify things here:
Lets take an unstoppable force, Gravity.
Now apply this force to any object, say a wooden board. Now lets say that board is leaning on the side of a large stone building.
Gravity is unstoppable, so because the board is leaning on the building due to gravity, it is infinity pushing at the ground and the stone building.
The building won't be moving any time soon because of that board, thus being an unmovable object. The board isn't just going to fly away, it's force, or weight, can only be redirected, such as if it falls over or is moved.
There ya go...