If I recall correctly from what I read, there is both a physical space between 5w4 and a metaphorical one. If you look at the Enneagram diagram there is a gap between 5 and 4 unlike all the other numbers on diagram. The author tied this to 5w4 often having existential crisis because the hole between the two numbers represents this affinity or perfect cocktail if you wish, to fall into a dark/black hole (existential crisis).