you might win three games, but lose four because of trolls and then be back at square one. My friend has been stuck between silver 4 and 3 and has been demoted, promoted, demoted, promoted.
Reminds my of Bjerg's demotion from Challenger then getting promos for it right after.
Luckily a high MMR makes up for losses so you end up where you belong even with more losses than you should've had.
This is season 5 in a nutshell for me.
Gold 2<->Gold 1
Ranked experience earlier today in a nutshell