Assalamu alaikum wa rahmatullahi wa barakatuhu!
In the Name of Allah, Most Gracious, Most Merciful
What is the point of slapping your cheeks or tearing your garment in sorrow over something you missed or some calamity that befell you?
What is the point in focusing your thoughts and feelings on some incident that has passed so as to increase your pain and make you fall apart?
If it were possible to reach into the past and change its events which we did not like, and alter them the way we like, then going back to the past would be essential.
We would all rush to go back and erase the things we regretted doing and increase our share of good fortune.
But that is impossible, so it is better for us to focus our efforts on what will help us get on with our lives, for that is our only means of compensation.
This is what the Quran drew attention to after Uhud (a battle named after a mountain in Madinah), when Allah said to those who were weeping for the slain and regretting going out in the battlefield:
Say: "Even if you had remained in your homes, those for whom death was decreed would certainly have gone forth to the place of their death" ..
(Surah Aale Imraan - Verse 154)
Be patient to be victorious.