"I'll take all of them"
I learned the term "splitting your wears" from Recovering Shopaholic, and I find it really useful to avoid overstocking basics. There are a limited number of times per week (or per month, or per year) that you're realistically going to wear any given type of item. When you have multiple items filling the same function in your wardrobe, they compete for time on your body. This is sub-optimal if your goal is to have a minimalist or capsule wardrobe, with no more than you need; or to avoid overbuying; or to drive down your "cost per wear" by wearing expensive items frequently.
Last week, I caught myself about to commit this error during the Fourth of July sale at J. Crew. I know that it's often a mistake to "shop sales" (browsing everything that's on sale, instead of looking for something specific). In this mindset, I'm just looking for anything I can use from the subset of items that are on sale. I noticed some lightweight cotton cardigans. Cardigans! So useful in the summer! So easy to add or remove from an outfit, and so appropriate for the office, where the air conditioning is high. Let's see, what color should I get? There's only one option from my palette, turquoise, so I'll go with that one.
Here's the problem: I already have a cardigan in a very similar color. I got it from Goodwill for $5 and I love it. I have no need to upgrade or replace it. Right now, I have the desire to wear this item between zero and two times per week. The one I have can easily handle that workload, so I don't need another. If I got a second one, I wouldn't wear turquoise cardigans more often--I'd just be dividing that zero-to-two times per week from one cardigan to two, unnecessarily. I'd just be splitting my wears.
Catching yourself about to split your wears before you buy something is the dream, of course; right now, I most often find myself doing it with things I've already bought and that are already in my wardrobe. Here are some specific different ways I've done it:
Functionally Identical Items From Different Brands/Stores
This is most likely the result of a situation very similar to the one I described above with the turquoise cardigan. I use the same thought process to buy almost identical items in two different stores at different times (often the result of sales or thrift store situations where I'm browsing a random assortment of items for "the type of thing I would wear"--which more often than not means the type of thing I already have!)
Same Item in Different Colors
When I really love an item, it's tempting to buy the same thing again and again. If I love one, more is better, right? Why wear my favorite shirt one day a week when I could wear it several times a week--in different colors, for increased interest? Finding my seasonal color palette has reduced this a bit since any given item is usually only offered in one True Summer color, but sometimes I have several options, and it's harder than ever to choose!
But something weird happens when I have three or four of the same item. I wear them less, even the one I originally liked. I get bored wearing the same item over and over, even in different colors.
Loving something doesn't mean you need more than one. Sometimes one is the optimal number.
Intentionally Splitting Wears To Preserve Something Nice
Sometimes I'll have a nice item, and a shittier version of the same thing, and I'll find myself wearing the shitty one all the time and the nice one never, because it's just a normal day and I don't deserve to put mileage on the nicer thing. This is "don't use the good china" syndrome that I discussed in my post on Overcoming FORO. At least in this case, it's obvious which item to get rid of: the obviously-less-good one that's standing in the way of my actually using the thing that sparks joy.
This is rarer and I actually think this is less likely to be a problem. If I am buying the EXACT SAME ITEM twice, it probably means I am going into it with eyes open. I have two copies of the exact same work dress, and I feel like this was a pretty good decision so far, since it means I can wear my favorite "little navy dress" twice a week, even if I sweat in it walking home. Some items lend themselves to multiples (underwear springs to mind), and some people like to have a "uniform," like how Mark Zuckerberg has a closet full of identical gray T-shirts and hoodies. For me, anyway, I'm unlikely to buy the exact same item twice unless I can actually use it multiple times per week, and I'm pretty good at stopping when I have enough. It's when the items are slightly different in some way (brand, color, etc.) that I trick myself into thinking I need more than I do.
Even though I don't keep records of how often I wear different items, so "splitting my wears" isn't driving any specific metric down, it's still a helpful way for me to think about how my wardrobe works, and so far it has helped me to avoid buying things that I essentially already have. I didn't buy that turquoise cardigan!