Recently I became interested in how suction cups work by creating a region of space with lower pressure than their surroundings, thus sealing the suction cup to the contact surface. Extrapolating this idea further, does this mean that a cube resting on a perfectly flat surface would be unable to be lifted since by doing so, you would be creating a region with zero pressure? Also, keep in mind that I'm speaking in purely theoretical terms and I understand that no object is perfectly flat and whatnot.
Even though real objects cannot be perfectly flat, they could be flat enough to stick together pretty well.
Common examples are two pieces of glass or gauge blocks wrung together (video). Besides vacuum action, other forces, like molecular attraction (adhesion) may play a significant role.