When more popular championship, that it widely is covered by media: TV, radio, newspapers, magazines, internet sites.
Media try to report in detail what is happening with athletes: desire to play, injury, motivation, etc. Such information flows have a huge impact on selection picks by bettors for betting and in many cases it leads to losing money.
For example. Team 1 is extremely necessary to win in team 2. If Team 1 wins, it will win championship, because is on second place now and two points difference of team 3, what takes first place. Team 3 has already played all matches, but team 1 has one match else.
Team 1 has high motivation for upcoming match, all players are in good shape and ready to play on 100% for required result. An additional benefit for team 1 is match at own stadium filled with fans.
Team 2 has some problems with starting lineup, several players are injured. Team 2 confidently took place in mid-table and upcoming match is absolutely nothing for them doesn't solve.
All media are talking about fact that Team 1 goes only to win and say a huge number of arguments.
Most of bettors in a similar situation bet money for team 1 victory because all stars came together for this. But as a result, team 1 loses match and all bettors lose money.
So, Thirteenth bettors mistake: betting based on public information.