1. Rav and Shmuel differed about whether one may cross a toll-way together with idolaters.
2. A person should not put himself in a dangerous situation with the hope that a miracle will save him.
3. A person should pray that he should not become sick.
4. Simple people die because they give denigrating nicknames to holy items.
5. The Gemara discusses why children die young.
A BIT MORE
1. Rav did not cross a toll-way when an idolater was crossing because he was concerned that the idolater would be prosecuted by the government due to his sins (against Hashem), and Rav would be prosecuted along with him. Shmuel would specifically cross when an idolater was crossing because he maintained that this prosecution happens only to people of one nation at a time.
2. If a miracle does occur, it diminishes his merits.
3. The Gemara explains that this is because a person who becomes sick needs to have special merit in order to be healed.
4. Rebbi Eliezer says that calling the Aron ha'Kodesh "Arana" ("cabinet") or the synagogue "Beis Am" ("the house of the people") is denigrating to those holy objects and can cause one to die.
5. A number of opinions are given. Among them are that children die because of a person's sin of not fulfilling his Nedarim (vows), a lack of Torah study, and not observing the laws of Mezuzah or Tzitzis.