Or, the effects could be set up so that the actual strength of a (eg. shield) part is the nominal strength divided by the total number of shield parts present, while leaving the nominal / UI indicated strength the same as if there was just one of the part present.
With the American Thanksgiving holiday nigh, I will share a bit of somewhat-related folk wisdom that's part of this cultural background (one that in fact is generally recognized as having continued validity although of course a game-theory risk analysis can make the calculus quite a bit more complex), which is, "A bird in hand is worth two in the bush."
Although of course there can be good reasons to simply discard a gangrenous or otherwise sickly bird, it seems to me that in the workings of our development there is a penchant for prematurely discarding the reasonable-but-not-ideal bird-in-hand in favor of pursuing the plumper/flashier bird glimpsed across the field, which unfortunately often never makes it into our bag, at least not that season. It's easy to think, "Putting this bird in the bag will get the bag messier than it needs to be," and, "we can just leave this caught bird-in-hand lying on a stump here, and if we give up on the nicer one we can come back for this," and, "if we let the hunters put the just-reasonable bird in their bag, they might put less effort into pursuing the really nice one." Those thoughts probably do have a grain of truth to them, but I would submit that it is such a small grain that it doesn't well support the full assertions, nor recognize their cost. Cleaning the bag after two birds is not much more difficult than cleaning after one. Also, after the discarded bird has been left weathering on a stump for a while it's much less appealing to head back to collect it, and people start to forget just where that stump was and even about the discarded bird at all. And then we have no bird at all for supper tonight.
Of course, folksy wisdom is rarely if ever dispositive, and perhaps in this case the bird-in-hand was sickly; it was a scrawny enough bird I won't argue the point. But I really do wish I would see these broader considerations at least acknowledged more often.
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