I don't understand why pressure changes the position of equilibrium in a reaction?

When thinking of pressure I like to think of two boxes joined together with the reactants in one and products in the other. When you make the boxes smaller (increase the pressure) the items in the box with more will start to be pushed into the box with less to reduce the amount of space in the one box. This is similar to a reaction!

N2(g) + 3H2(g) <-> 2NH3(g)(would be best written on the whiteboard for super/subscripts)

As we increase the pressure we will see the reactants 'move to the box of products' because there are more molecules on the side of reactants. They move to make more space by becoming products!

Now think of 2NO2(g) <-> N2O4 (g) what do you think would happen if we DECREASE the pressure?