Imam ‘Ali (a.s.) said:
لاتُشْغِلْ قَلْبَكَ الْهَمَّ عَلَى مافاتَ فَيُشْغِلَكَ عَنِ الاْسْتِعْدادِ بِما هُوَ آت.
Do not preoccupy your heart with grief for the past because you will lose out on preparation for the future. 1
One comes across two groups of people. Some of them waste their time regretting for the past mistakes and lose their remaining energies in this way. But others let bygones be bygones and only take some lessons from them for organizing the future and use all of their powers constructively to build a better today and tomorrow. Surely, they will be the ones who will succeed.