Was anybody else ever surprised by how slow the characters are and how often the story is spoilered for either you or the characters by another character and they later act like they didn't ever hear anything about it, which is almost a plothole.
Tidus sees Seymour when they leave Mi'hen:
- He never actually trusted Seymour in the first place but he thought at that point he was right
=> Already spoilers Seymour is later revealed to be something not expected by Seymour to be found out at that point; Tidus should not talk in Flashbacks like he already told people Seymour was a villain.
Seymour finally becomes more active as a villain (visibly):
- Seymour is all "Lady Yuna, come with me and sacrifice your life and I will become the next Sin", which already spoilers both the characters and the viewer that a person who follows the summoner becomes Sin. And yet they act like "What? We never knew!" (except Auron) when they meet Yunalesca.
Seriously, they knew the Final Aeon becomes Sin, what did they expect Seymour to mean to still be that surprised later? Did they thought Seymour was just making things up or that he simply was able to do so because he was who he was (something not that far off for a Final Fantasy villain but Seymour did nothing up until this point to show that he could do something like that; he then started absorbing souls and later even wanted to actually become Sin without being a fayth but the latter was after his plan to join Yuna which was another way to achieve his goal and for that way that he revealed first they should have at least thought anything). Also the whole controlling Sin thing would have only worked by either absorbing Yevon=Ju or having such a powerful will to make your mind the new mind of Sin, with full control. Something he did not plan exactly like that at first, as said getting control without Yuna was his later plan. Yuna and Wakka are proven, partly even called to be naive, but the characters are not totally dumb. "Join me, sacrifice yourself and let me become Sin" is pretty much as obvious as it gets to be honest. The viewer might not think that far at first but the heroes who are in constant contact with such a presence and know why it is still here should find that out from Bevelle to Zanarkand. And Tidus even had the information that Jecht, who was Braska's guardian already, became Sin, so he knew a guardian became Sin. That with Seymour's comment together should have been enough to tell him "oh, crap, apparently this is a thing for every summoner normally" - or to be more precise, a person normally does it who follows the summoner and is okay with doing that. And normally only the guardians follow them to protect them so they are those who do it in most cases. I have been confused by this for about 10 years now as I cannot believe they didn't get it but were so shocked later.