The amount of a particle's energy can change drastically in a short period of time, as long as it maintains it's average energy. Hence it is possible for a particle that averages a low energy to momentarily "borrow" enough energy to go through a barrier. This is called quantum tunneling. The likelihood of this occurrence depends on how much a particle's energy must increase to go through the barrier. This means that a human could go through a wall, but since every particle inside of it must be lucky enough to gain enough energy at the same time, it is highly unlikely. You would need to walk into a wall once every second for longer than the current age of the universe to have a good chance at passing through it once. Even in an empty area of space, energy fluctuations can occur that converts into matter (through E=mc²) to create an electron and its antimatter counterpart the positron that quickly disappear when the energy is "repaid".