Demotion

its not number based. its "how high is your MMR, and whats the average player you're playing with"

if you were truly average rank, primarily silver 2, you always play with silver 2 players. and you just manage to scrape out a win streak and climb to silver 1. on your first few losses from zero you would get kicked back into silver 2. ( i believe you have a 3 game grace period to prevent falling and having to do promos again)

but if you're playing with gold 3 players per say, you wont ever get kicked out with a 50-50 win rate against them. you'll stay silver 1 even at 0 LP.

until you lose lots of games and your MMR starts to tank and you are losing even against silver 1 players. then you'll fall back to silver 2.