There is an occasion when should not rely on one’s Rabbi – and that only occurs on a Wednesday or Thursday! When the first day of (a two day) Yom Tov occurs on Thursday or Friday, then on erev Yom Tov, namely Wednesday or Thursday, one makes eiruv tavshilin. Although the Rabbi of the city includes all the Jews in his city in his eiruv tavshilin, one should not rely on this but should make eiruv tavshilin oneself; it can even be problematic after having relied on the Rabbi on a previous occasion. So don’t rely on your Rabbi on this particular Wednesday or Thursday!!  (Shulchan Aruch, Orach Chaim 527:7)