New players start unranked and join the ladder after their first win. Beat someone ranked above you and you jump halfway to their rank. Beating someone below you changes nothing - there's no reward for farming weaker opponents. Losing doesn't move you down, unless you lose to the person directly below you, in which case they leapfrog you. Gone quiet? Sitting out for 3 days drops you 3 places, and keeps dropping you another 3 for every further 3 days you're inactive - nobody camps at the top by just not playing.