here are the possible reasons:
| smurfs (enemy team)
| own skill loss (defeats)
| enemy skill gain (defeats)
| own skill loss (changing the % bracket rank cut off)
| enemy skill gain (changing the % bracket rank cut off)
| influx of new skilled players (on enemy team)
| influx of new unskilled players (on your team)
| ladder dilute (huge numbers of new players changing the % bracket rank cut off)
| bordom (games randomly thrown by experamental tactic of key players)
| entropy (games randomly lost due to ingame conditions.. accidents, bizzare situations, massive reclaiming, wrong timing, wrong placement..)
in real life its like carring around an umbrella.. then the one day you dont bring it; it rains... sometimes its just impossible to plan for every situation. the ranks are supposed to avergage out these annomelies so long as you play for a long time