Games : How does Riot decide which tier to put you in after the provisionals?

So as we all know, we need to complete 10 provisional games at the start of a new season to get into a tier (Bronze, Silver, etc.).

Some people manage to win all their 10 provisional matches and get into only Bronze or Silver, whereas, some people only wins like half their provisionals and still get into Gold tier.

How does this work exactly?