While halacha often expects that you get things right the first time, there are cases where one can remedy an error made. One example of this is tashlumin, where if one misses davening (or, originally, a korban), there are opportunities to make it up later. This only applies for a limited time frame – if you miss shacharis, you can make it up at mincha, but not later. Similarly, if you miss havdala Saturday night, you can do it until Tuesday, but no later. And sometimes you can’t make up what you missed. On some views, if due to reasons out of one’s control, one cannot fulfill a positive mitzvah, they have missed out and cannot remedy that at all.
Maybe the best example of second chances is pesach sheni, marked on the 14th of Iyar. If one is tamei or far away and didn’t bring the korban pesach, one can bring the pesach sheni a month later. Bamidbar 9 tells us the origin of this halacha – there was a group that was tamei and missed out. Sad to miss the mitzvah, they approach Moshe and ask him to participate, asking “lama nigara” – “why should we miss out?” Due to their commitment to fulfill this mitzvah, the Gemara tells us that they receive credit for establishing it, as even Moshe forgot this teaching.
