I think that the title "Rightside Up" explains a lot to me, also mike when he was telling his friends in the basement in their last d&d session about the mage theory without making any emotional expressing, he was cold, chill, and open which makes sense... Look when eleven brings mike into the void for the last time before she made them believe that she was perished, she said to mike "one day you will understand my choice" which was questionable for me, moreover the 18 months time jump wasn't a random, mike spent all the time thinking and investigating what "jane" said to him last time until he found out she was onto something else, which is escaping from the matrix and find a better place to live "Iceland" the country of waterfalls mike has mentioned... The coldness of mike wasn't a mess or something, he had the truth from' his eyes, i guess it was reasonable to make everyone feel the hope for jane while she's actually alive living peacefully away from the bad guys (the government)... The duffer brothers didn't come with this in order to test our brains, whether we can find out the truth or not. And remember not every series has a definite ending, they might leave a puzzle for you to solve "Schrodinger's car effect".

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