What changed? The only thing that matters in League - my attitude/mentality.

Not quite silver, but was plat in S4 it's not that big of a difference. I started playing in S2 and for the first 2 years I had the classic low elo mentality (unlucky teammates QQ not my fault etc.), which obviously blinded me and prevented me from improving. Once I started focusing exclusively on myself, playing to improve and ignoring wins/losses/LP/promos and most importantly what my teammates were doing/writing I started improving, enjoying the game way more and climbing. I'm still trash, but much less so than I used to be. I reached D2 soley thanks to getting into a proper mindset.