In Paradox, Praedyth mentions that Pahanin was always talking to himself. This is actually Pahanin talking to the Super Good Advice, a gun which in the lore could talk to its owner. Just a fun little touch I noticed.
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I think you've got it a little backwards. All lore points to Pahanin making SGA after becoming paranoid from the events in the vault. Likely, he always had some fear issues and talked to himself as a means of coping. But the events of the vault traumatized him and forced him to build something that talked back so he would never be alone.