When Aaron’s wife, Elisheva, heard the horrific news about her two son’s she was grief-stricken. Tehillim teaches us (75:5), “Do not make merry (Even if you were tzaddikim-righteous men) and all the more so to the wicked, Do not lift your horn!”
In other words, Hashem warns the Jewish people not to be lightheaded, for a person who is well off today, will not know with certainty what his life will bring him tomorrow. Even the greatest tzadikkim face hardship and misfortune. Conversely, a person who suffers today, his fate may be completely shifted tomorrow. Our fates are fluctuated continuously by Hashem, each day has something new in store for all of us. King David wrote this psalm to remind us not to overindulge in happiness because complete joy does not lie in this world, rather in the next.
Why would Hashem create a world of tragedy and grief? Unfortunately, people easily forget reality. We tend to fall asleep spiritually and become completely absorbed in fulfilling our physical desires. This spiritual blockade makes us become completely self-reliant and arrogant, essentially we forget Hashem. As we continue to attain our physical wishes, we lose sight of the frailty of our existence. When misfortune comes our way, it is used to remind us how frail we really are and how we owe our entire existence to a higher source- Hashem. When one is struck with misfortune, it is meant to be used to develop our humility and as a means to get closer to Hashem, the trick is figuring out how.