For me, making connections with other people is part of me, not something I actively choose to do. In that way it's the same as my sexual orientation, in that it's not something I consciously choose.
But I do choose what to do with those connections. I could choose to keep them all at the level of friendship without any physical involvement and live in a mono relationship. I'd survive and probably be happy enough. But luckily I know myself well enough that when MC and I started dating, I said upfront that he needed to be able to accept and support my flirtations and FWB's or our relationship was not going to work. So I don't have to make that choice to be strictly mono.
However, I didn't really CHOOSE poly either. It just sort of happened. TGIB was a FWB who became something more. I was lucky that, though we hadn't expressly discussed it previously, MC was not threatened by me developing a more serious relationship with TGIB. I suppose I could have been considered open to poly, since I'm not a fan of forcing relationships to fit predetermined definitions, but I kind of feel like poly chose ME, rather than the other way around. I was never LOOKING for another serious LTR besides the one I have with my husband, so I can hardly say it was a lifestyle choice in my case. It's a choice NOW, so MC and I can have this amazing person in our lives permanently, but even now that I know so much more about poly and the different ways it can work, I don't think of myself as "practicing polyamory". The three of us just figure out what works for us and call it good. (I also no longer have much interest in flirtations or FWB's. I'm polysaturated with my two guys, thankyouverymuch!