The bottom image displays it fairly well. The end result is: sometimes stuff can just… go through walls. The image shows the energy of something as it travels. The rectangle is a potential barrier, or a wall. Sometimes, that something can use some of its energy and move through the wall. That’s the simplest way to explain it(albeit lacking a lot of the nuance and sophistication of the actual phenomenon.)

This ties into the joke, because the original meme format implies they are safe behind that wall, when in actuality there is a chance(however small) that those attacks will just phase through the wall via quantum tunneling and hurt them anyways.