As I get older, the chill that starts this time of year gets harder to bear and seems to start earlier. No, I do not mean the weather; I can dress for that. I mean response from my wife when I mention that I am learning hilchos Purim; because Purim starts with P and that rhymes with P and that reminds her of Pesach, right here in River City. I tried to ease into it by saying I was learning about hilchos Adar, but she's on to me.
Halichos Shlomo says that Adar is different, so it is ok to make a chasuna right up the the end of the month. I might as well have read, "it is permitted to stir a milichig pot with a milchig spoon." Fortunately, the footnotes sent me to the Rema on Shulchan Aruch, Even haEzer 64:3. Sure enough, the Rema says the minhag is not to make chasunas near the end of the month. Apparently "end" means after the 23 or so. We made on on Rosh Chodesh and one on the 12th, so -- whew -- we were fine. When asked, R' Shlomo Zalman Auerbach said it's a good idea to be careful; there are lots of days to make a chasuna, so why choose one with bad mazal. Apparently one talmid was not satisfied with that and asked, "But didn't the G"ra make a chasuna for his son a the end of the month and say that now-a-days we can do that?" R' Shlomo Zalman responded that, yes, but it is very hard to go against the Tur and Shulchan Aruch who say not to.
The problem is that our sensitivity to the spiritual dimensions of the seasons is very blunted. What would be the one day of the year to definitely not say tachanun? Purim, right? Yet, there is a shita in the G'onim that one does say tachanun on Purim. (We don't hold that way, but it shows how close a call it is.) On the other hand, everyone agrees that on Tisha b'Av -- the national day of mourning -- we do not say tachanun.
In fact, there is a logic to those halachos. Purim is the national holiday of confirming our acceptance of the Torah out of love. It is precisely that day, therefore, that the loss of the Beis haMikdash (may it be rebuild soon and in our lifetime) is felt most acutely. On Tisha b'Av, at the nadir of our experience in galus, we are encouraged because we know it can't go worse... that day and the national repentance are the seeds of the redemption.
Why did the G"ra do something different that stated in Shulchan Aruch? I couldn't say. At the end of the day, though, we have a mesora for what t'filos to say on what occasions. That's our mesora, that's our guide.