Life is full of second chances. If I didn't watch the game live, I can always watch it on my Tivo. If I "forgot" to pay my taxes, sooner or later the IRS will grant me an amnesty period to correct any oversight I might have made. Second chances give us the opportunity to make amends for errors or oversights we might have made.
Beha'alotecha gives us the Torah's most prominent second chance: Pesach Sheini. Those people who were tamei (ritually impure) during the offering of the korban Pesach approach Moshe with a problem. They missed out and want to offer the sacrifice. לָמָּה נִגָּרַע, לְבִלְתִּי הַקְרִיב אֶת-קָרְבַּן ה' בְּמֹעֲדוֹ -- "why should we be kept back, so as not to bring the offering of God in its proper time." (9:7) Moshe, repeats their request to God who answers in the affirmative, telling Moshe about the law of Pesach Sheini (the second Pesach). Essentially, God gives them a second chance, commanding pretty much anyone who did not bring the korban Pesach at the proper time to be sure to bring the offering the second time around a month later.
I can think of only one other case in Jewish law that deals with second chances. The gemara in Berachos teaches us that if a person forgot to recite a given Amidah or was prevented from doing so, he may "make up" that prayer at the next opportunity. Essentially, if I forget or cannot recite Shacharit on a given morning, I can (and must) recite two shemoneh esreh prayers at Minchah time; the first counts as Minchah, and the second counts as the Shacharit I missed that morning.
Yet, these examples have always left me wondering: why are these the only two prominent cases of second chances in Jewish law? If I forgot to eat matzoh at the Seder, or shake a lulav, or light Chanukah candles at the proper time, halachah offers no mechanism for me to make up those mitzvot. Why not? What's unique about the korban Pesach and prayer that demanded that we all get a second chance?
To my mind though, second chances have an even greater cost. If you can always do things over, that ability to repeat robs the event or activity of its meaning and import the first time around. Why bother trying very hard on my golf shot if I can just take a mulligan? Why make the effort to light candles on time if I can just do it next week? From this perspective, having a second chance isn't always the greatest blessing.
I most cases, you have to get it right the first time. Because there won't be a second chance.