When he saw that I couldn't open the door I asked him what the trick was he said, in a tone of voice that made it sound like this was obviously something everyone should know, you need to pull the door before pushing it. The door was wedged such that the easiest way to open the door was to pull the door as tightly shut as possible and then immediately shove the door open. This friend, since he grew up in that house, thought this was obvious, apparently not realizing that it's not normal to have to try to close a door extra hard to open it.
This "missing stairstep" analogy is appropriate here, though that metaphor is most commonly associated with a very specific type of problem involving guys who are creeps.
As it relates to the broader context of technology that this piece situates this anecdote within, it could be considered a form of implicit step zero or an analogy for developer tunnel vision.
