"[It is hard to know what is good luck and what isn't and therefore whether we should be happy or sad about it. Only time will tell. For example...] The Talmud relates a story about two people who wanted to travel by boat. One broke his foot and was unable to make the trip, while his friend got on the boat. The one who missed the boat cursed his misfortune. A few days later, however, he heard that the boat sank and all the passengers drowned."