Gam Zu Letova verses Letav Avdin:
The Gemara states that every person is to accustom himself to recite “Kol Mah Deavdin Min Shemaya Letav Avdin/Whatever is done from Heaven is done for the good”, as was seen with the story with Rebbe Akiva. Elesewhere, the Gemara states that Nachum Ish Gam Zu would say Gam Zu Letova. What is the difference between these two statements? The explanation is as follows: Every punishment or act of suffering has an aspect of Chesed in its root. A person who finds this Chesed ends up sweetening the Gevuros, and immediately turns the the severity to kindness. This was the level of Nachum Ish Gamzu. One however who does not know the aspect of Chesed contained within the severity is to say the previous statement.
 Keser Shem Tov 33
 Brachos 60b
 Taanis 21a