Great thread! I think I have a bunch of danger zones. I'm probably forgetting a few, but here are some:
Heeled pumps for work: For some reason, I don't wear these as often as I think I will. I'll gladly wear other types of heeled shoes, as well as flats or wedges with the same basic shape as a pump, but my pumps usually feel a little frumpier or fussier than other options. It probably doesn't help that I look for pumps that will be comfortable all day, which may push them towards frump to begin with. And, even worse, I keep looking in my closet and seeing a bunch of pumps I don't wear much, which means I rarely feel like I can justify buying heels I really love for dressier occasions. Not that I need that many for my life, but I could probably use more than I have.
Non-neutral camisoles and layering tops: I have a bunch but, most of the time, I'd really rather grab a layering top in the most obvious neutral and concentrate on some other part of my outfit than worry about what the perfect color is for something that just peeks out a little at my neckline.
Practical-seeming blazers/jackets: I actually posted a K/T thread with some of these a few days ago! I don't wear blazers much but, every so often, I'll decide I should and buy one that checks all the boxes - versatile color and style, fits well, and is a good deal for the quality. Then … it sits. I think I have been getting better about avoiding this lately though. At least on the buying-new-ones end of things.
Anything casual that needs a belt to look good: I'm way too comfort-oriented to deal with the feeling of a belt around my waist if I'm not at work or going somewhere where I want to look especially nice.
And I really relate to Jules with regard to the dangers of shopping at the ultra-low end. In particular, this sounds familiar: "My epiphany was that I need to shop higher end more often not because I necessarily appreciate higher quality but because I am so much more careful with my selections when I am spending real money."
With me, it's even worse when I'm shopping somewhere cheap that also involves a lot of filtering to find something I like for myself (e.g, at Forever 21, sometimes at consignment stores). When I've gone through a lot of effort to yield one thing that works, it's really hard to tell whether that one thing is amazing or just sort of serviceable.