Boil It Down!
Back in high school (feels like centuries ago!) I took several years of French classes. For some reason I still remember two unrelated and random phrases. The first is "ferme ta bouche" (a rude way of asking someone to shut up), and the second is "raison d'être." I've had many fun opportunities since then to make use of the first phrase (four rambunctious little ones will easily draw that one out of you), but only lately have I been thinking more about the second. Your "raiso