Lingerie Regrets

With the exception of a few bob in my bank account, the change pictured here is all the money i have right now. Moving apartments and the steady decline of shifts at work due to the summer months have contributed to my incredible lack of money. So until the day my student loan rolls in and frees me up a little, i'm pinching the pennies. Something i've been doing to wise up on my spending, is going through my lingerie. I've identified that i have a big problem with buying lingerie that never gets worn. In fact i have such a problem that i can actually categorise my recurring mistakes into one of the following:
Size.
This is by far the most ridiculous problem of my lingerie hoarding and tends to intensify around the sales. I've been known to splurge on sizes considerably larger than my own by convincing myself that i'm secretly a 34B (or something equivalently dumb like pretending my arse is a size 6). Considering my whole life revolves around logical thought, in particular when handling numbers, i'd say this is a pretty embarrassing problem. So i buy the underwear i really want, in a size that will never fit me, and it, quite rightly, sits in my lingerie box (oh y'know, the one us hoarders have specifically for bras and knickers that don't fit) indefinitely. Clearly i need to tackle my impulse buying.
Shape.
I'm aware of the shape of my chest, very much so. But it doesn't stop me buying bras that are quite obviously better suited to a different shape. The bra pictured was a cheap ebay find but i should've known straight off the bat that this bra wouldn't fit. The lace at the top has nothing to sit flat against, so bunches and gapes and the cups hold their largest volume closest to the centre gore so they gape as well. All in all i did an exceptional job at forgoing all logic in the eyes of a pretty, cheap, bra. The shameful thing is that i never seem to learn and i own a fair few bras with exactly the same problem.
Practicality.
It's scarily easy to blindside me to practicality. If it's pretty, cutesy or unusual i'll always tend to completely forget how utterly useless the garment will be. 
This garter belt is one of the only "extravagant" pieces from Topshop's lingerie line that i've actually splurged full price for. I'm such a sucker for a white/pale pink colourway, especially if it has bows and frills. What i completely forgot is that i only wear garter belts when i'm wearing thigh highs. And i only wear thigh highs under my work clothes. Clothes which just so happen to be tight fitting. So the frills and the embellishments are highly impractical unless you're a fan of looking lumpy. Which i am not.
This AP bra, albeit utterly gorgeous, is completely unwearable in any practical sense. If someone would care to enlighten me as to what purpose a demi bra actually serves i'd be very grateful. This bra is a perfect colour, gorgeously constructed and fits like a glove. But what use is a bra that doesn't fully encompass my nipples and looks particularly strange underneath clothes, seriously? And most importantly why are all the high end bras i want demi?
Comfort.
I have so many of these bras (and knickers). They look comfortable, and feel absolutely cosy the first time you try them on but two hours into a six hour lab session and you find yourself counting the change in your purse so you can catch a bus home to change. Yup, this Boux Avenue bra has proven to be so uncomfortable that i can't bring myself to wear it for any longer than a couple of hours. Sometimes i like to look at it forlornly, and remember the high hopes i had for it to join my summer wardrobe. Unfortunately i'm no fortune teller, so i can hardly spot an uncomfortable piece of lingerie before i've even worn it. But it's something to take into consideration anyway.