While the simulation argument may seem complicated at first, we can examine each case of the trilemma to show that one of them must be true (at which point we'll take a closer look at one such potentiality). First, let's start by examining case 1.

Case 1. Civilizations that have reached our modern era of technological development go extinct before reaching technological maturity (e.g. reach a 'post-human' state).

Case 1 states that as technology continues to mature, civilization converges on extinction. There is no particular causation given; a common example cited is that an ultimately self-destructive technology is developed. If this proposition is true, then neither case 2 nor case 3 can occur, as civilization never reaches a technologically mature/post-human state. That is to say, we can never become post-human nor can we be part of an advanced simulation if the truth is that we will ultimately go extinct first!

Case 2. As civilizations approach technological maturity they lose interest in developing "Ancestor Simulations" that would, in a technologically mature civilization, be advanced enough that entities within the simulation would have consciousness.

Case 2 supposes that it is possible for a civilization to reach a post-human state of full technological maturity. In this particular context, technological maturity refers to technology advances reaching the point that no further advances in technology are feasibly possible. Assuming that reaching this state is possible, the case further suggests that this post-human civilization will not be interested in what preceded their existence (e.g. their ancestry), perhaps as a side-effect of knowing all their is to know about their universe.

Case 3. We are almost certainly living in a computer simulation.

Supposing that neither Case 1 nor Case 2 are true, then we are supposing that it is possible both that a civilzation can advanced to a post-human point of development and that upon reaching such a state said civilization would still have enough interest in their forebears to develop simulations of them. First, recall that in this post-human reality simulations are advanced enough that simulated entities are advanced enough to posssess their own consciousness. If such a case is true, then it is not unreasonable to assume that simulated civilzations could also reach a post-human state to and conduct their own simulations. This assumption propogates further and further down, to the point where there are inifinitely many simulated realities. In this case, then, it is much more likely we live in one of the infinitely many simulated worlds than in actual reality.