Why should we not get upset or feel exultant due to any bad or pleasant incidence?

 

Verses 22-24 of Chapter 57:
No affliction befalls in the earth or in your own selves, which We have not recorded in a Book before bringing it into being. This is an easy thing for Allah, (This' is done so that) you are not disheartened over what you may lose nor feel exultant over what Allah may give you. Allah does not love those who are arrogant and boastful, who are themselves stingy and also urge others to be stingy. Now whosoever turns away (should know that) Allah is All-Sufficient and All-Praiseworthy.