The Shulchan Aruch (Code of Jewish Law) states: "A person should acquire the habit of constantly repeating [Rabbi Akiva's Talmudic statement]: 'Whatever the Almighty does is for the good.'" (Orach Chaim 230:5)
Imagine a day in which everything went well. Every conversation and transaction with others went exactly as you would have wished. All the hundreds of daily tasks and routines you engaged in worked out to your complete satisfaction. How would you feel? Extremely happy! (Unless of course you ruin it for yourself by worrying that perhaps in the future things might go wrong!) You'd probably be in such a good mood by the end of the day that trivial irritants would not bother you in the least.
Living with a Torah perspective means that every event that happens to us throughout the day is for our ultimate good. If we would internalize this concept, our standard mood would be joy!
(see Gateway to Happiness, p.65)