I've always considered myself to be both British and Irish. I've been entitled to be an Irish citizen all my life by virtue of having been born on the island of Ireland; but since I was born in Northern Ireland, I'm also a British citizen, and so by a subtle quirk of Irish law I wasn't automatically an Irish citizen. To actually become one I had to do something that only an Irish citizen is allowed to do, the most obvious of which is to get an Irish passport, and I've been meaning to get round to that for years ...
So, as of today, I finally hold a pas Éireannach, and I'm legally a dual citizen. (And it's remarkable how much less ratty it is than my British passport which has spent more time than it ought to have done in a trouser pocket!)
When I talked about intending to do this before, people sometimes asked me why I was bothering. After all, both the UK and Ireland are in the EU, and neither is in Schengen, so there's no functional difference between them; I expect I'll travel on my Irish passport from time to time, but I don't expect it will have any practical effect (although an apparently very confused US immigration official once grilled me about why I wasn't travelling on an Irish passport when I was born in Belfast).
Firstly, I want to: I feel an attachment to both countries. Granted, I've only ever lived in the UK, but in some sense that's an accident of century-old politics, and I feel at home in a different way when I'm in Ireland.
Secondly, I think that if you have privileges extended to you by governments then it's generally a good idea to take them when you can.
Thirdly, my children may want to claim Irish citizenship themselves. They should be able to do so (and, under current law, so can their descendants, indefinitely as long as they keep registering foreign births), but that will be a lot easier for them if I've done the paperwork.
Fourthly, it does not seem outside the bounds of possibility that at some point in my lifetime the UK will have a hissy fit of some kind and leave the EU. I'd rather it didn't, but it's possible and it's not like I'd be able to do a whole lot to stop it. If that happens, there are obvious practical reasons why I'd want to remain a citizen of the EU, and Ireland seems much less likely to leave.
Anyway, rational or not, I'm happy to have finally got this done!