Flexi Says: When your hand is pressed against a wall, all the electrons in your hand have to replace all the electrons in that part of the wall to be able to pass through it. However, in the case of electrons, Pauli's exclusion principle that no two things cannot be at the same place at the same time, holds good. This causes electromagnetic repulsion between your hand and the wall and prevents your hand from passing through it. Owing to this reason, although most of the atom is empty space, it is impossible to stick your hand through a wall under normal conditions.
