Hi Jae. Thanks for the question.
You do not need to have a direct link between every pair of related notes, just like you don’t need a dedicated road between every pair of cities in a country to travel between them. It’s OK if you get from one note to another related one in two or three hops. Moreover, you don’t have to add all of the links at once.
So what you do is you create a new note and then link it to its most obviously related ones. If you keep doing this, you will always be able to reach every other related note in very few steps.
This is related to the idea of 6 degrees of separation: All 7.7 billion people on this planet are connected by at most six friend-of-a-friend links. That is, you can take any two random people on this planet and get from one to the other in at most six steps if you keep getting in touch with a friend of a friend of a friend… up to six times.
You won’t have 7.7 billion notes. But even if you had, according to the 6 degrees of separation, you probably could go from any note to any other in just a handful of steps as long as you keep connecting those notes that are most obviously connected.
Moreover, if while exploring your Zettelkasten it took you a few steps to get from note A to note B and you then notice that A and B are actually strongly related, you can just add a dedicated link between A and B at that time.
I hope this helps :)