I want to create a cut in a cube so as to create a hollow pool of water in the middle of the cube. However, when I apply the boolean modifier and remove the object used to cut into the cube, I see no actual difference. The cube is still completely solid. Only in edit mode can I see that a boolean operation has been performed, but unfortunately no hollow area is created. I hope someone can tell me what the issue is here.
The problem is the topology of the small cube, it is made of separated faces, so the Boolean operation can't work properly. To solve this, you need to go in Edit mode, select all, and W > Remove Doubles, so that it joins all the faces together and make a real cube. Then your Boolean will work properly.