Placements

I win 7 games in a row in ranked, including unranked, the number is WAY higher. But then I lose 2 consecutive games in ranked and get placed in bronze 1 when I was formerly silver 2. I have heard of people going 4 and 6 in placements and getting silver 2. But that just doesn't make sense to me though.

Can someone explain to me how that is possible?