I've been thinking about the ending of SOMA and it's really wonderful that a game can make you ponder so many things even when you're not playing it. Frictional Games have done a great job with this one. Here are some brief thoughts and interpretations of it after my initial playthrough.
>>Different versions of Simon
In SOMA there are ultimately four versions of Simon:
Simon-1 (Toronto) --> Simon-2 (First Suit) --> Simon-3 (Second Suit) --> Simon-4 (ARK)
Who experiences continuity and when?
Simon-1 = never
Simon-2 = remembers a 'jump' from v1-v2
Simon-3 = remembers 'jumps' from v1-v2 and from v2-v3
Simon-4 = remembers all of the 'jumps', v1-v2, v2-v3, v3-v4
Which jumps do you, as the player, remember? V1-v2 and v2-v3. Therefore, YOU ARE SIMON-3. Your 'real' existence begins when you are loaded into the second suit but you still have a recollection of previous events and thus you experience continuity. So: everything up until the second jump are just your memories. We play through those events because they're a part of Simon-3's subjective experience that he remembers (even though he, in this version, hasn't actually experienced them first-hand).
The only time the game 'switches' between different versions of Simon is in the Post-Credits sequence.
>>Cognitive bias
That also provides a reason as to why Simon is led to believe that he will 'carry over' to the Ark. Because he 'remembers' being 'carried over' twice already. He's convinced that he'll 'jump' to the Ark because in HIS subjective experience, HE carries over, not 'the other Simon'.
And why is it that he somehow misses the facts provided by Catherine? Because of his
cognitive bias. In Simon-3's subjective experience (or recollection of it) he's the one who 'carries over' everytime and this deeply rooted emotional conviction overwrites the factual evidence. This kind of behaviour is actually common in real life. Perhaps Simon is just too realistic, too human for a video game and that's why some question his behaviour.
I mean, he remembers 'jumping' from one suit to the other, just an hour ago - surely HE carries over, right? He's been experiencing continuity all this time so why would it be any different now?
That's why he never actually grasps that he'll be left behind until it's too late.
>>Player versus protagonist
This also brings out the problem with the player-protagonist sync, unfortunately. Some say "well, he knew this would happen so why is he angry?" The problem is that players are comfortably sitting in front of their monitors, having all the time in the world to process and analyze the critical information. Simon is terrified, going through a tremendous amount of stress, torn apart by thoughts of his identity, plus there's a bias shrouding his judgement. Players, even those heavily immersed, do not go through the same kind of experience so some might not be able to identify with Simons emotional state.
I personally love the ending, though I maybe wish the Post-Credits scene never happened.