The thought that juries being "bitter" cause the "best" player to not win is, for the most part, ridiculous. Certainly there are some situations where a player will delusionally think that they deserved to win more than the "best" player and therefore, vote against them. But for the most part, players are are "bitter" as a direct result of how they were put on the jury.
Unlike boxing or gymnastics, where the people that judge have a specific set of criteria they are judging on, there are no concrete rules or guidelines for the juries on Big Brother (or Survivor) to base their votes on. You are basically voting on who you think deserves to win (or against someone you think deserves to lose) based on each jury members personal idea of who deserves to win.
Therefore, the biggest part of these shows are how they put the people on the jury. If you promise someone, something more than what you actually give them, it's certainly going to affect their vote. If you make final 3 deals with multiple people, everyone that doesn't make the final 3 has a reason to vote against you. It's not bitterness, it's the players own fault for not living up to their own expectations.
I remember Dan Gheesling and how so many people were up in arms over him not winning, and the jury being so "bitter". If you recall, Dan made multiple promises on his "family" his "marriage" and "the bible". And broke them. It's up to each person do decide if this is ok, as just gameplay, or not. If you build a personal relationship with someone, and then burn it down, sometimes you don't get to just say "it's just a game" and get to win. If you misjudged how that juror would take what you did to them, that is your own fault.
Look at this season, only 4 of the jury voted for Paul, in a season where many of you think that he played the best game. Of those 4, 1 voted basically because her best friend voted her out (Xmas) and the other 3 are arguably the 3 people that least played the game. Raven is completely delusional, Matt was probably disappointed when he opened the key bag that there wasn't any cereal in there and Kevin...I mean, god bless Kevin, but the man had no clue about Big Brother or what it was about.
To conclude, I submit that, in most instances, "bitter" juries are mostly the fault of the finalists. It is unfair, to be on the outside and call a jury bitter, when you weren't involved in the game. The finalists set their own fate, by how they put the players in the jury.
P.S. Don't think this comes from a Josh fan. I think the dude is a joke of a human being. He had absolutely nothing to do with the outcome of this season, every vote on that jury was either "for Paul" or "against Paul" (with the exception of Xmas...which, lol).