Winning Spree v Losing Spree

What are their triggers? how do they come about? -Some would say if you play well you go on a winning spree, but we all know that's bullshit -Some say if you play badly you go on a loosing spree, again we all know that's bullshit -Some say you are being placed vs better enemies as you climb, but how are they better when they should match my MMR? We should be equal in skill same with my teammates, all of us should be equal or very close in ratings. Some say riot gives you players with lower rating to balance it out but that doesnt make sense as it's supposed to match you with players of equal level So how do winning and losing sprees occur? how can some1 go from 7 win in a row to 4 losses in a row and vice versa? Better opponents? worse teammates? you magically started playing badly? For me the only thing I see change are my teammates, the enemy team doesnt feel more difficult but my teammates feel worse.