MW Murphy's Law #30: Whenever a situation arises which can only be handled by one party member, the player responsible for that party member will stop posting for an extended period of time.
MW Murphy's Law #31: When collecting loot from a dungeon, or after winning a difficult battle, at least half of the awarded items will be set aside, ignored, and sold at the first opportunity. The most useful or most powerful item in the bunch will always be one of the rejects.
MW Murphy's Law #32: Characters with below-average intelligence or wisdom (or both) will always fall into one of two categories: MacGyver, or Leeroy Jenkins. Either the character will conveniently ignore the fact that he shouldn't be smart enough to think up the brilliant strategies he constantly uses, or the character will intentionally use his stupidity as an excuse to derail the plot and endanger his allies.
MW Murphy's Law #33: When recruiting new players to a game thread, at least one of those accepted will always be the GM's least favorite type of player (powergamer, essay writer, clown, rules lawyer, etc.) No known screening method is capable of preventing this.