I keep a little tray by the front door, the sort of thing you buy with good intentions and then use as a dumping ground, and most mornings I’m stood over it deciding which scarf or which sunglasses are going to rescue an outfit I didn’t plan properly. Half the time it’s not the coat or the dress doing the work, it’s whatever I grab off that tray on the way out.
The difference between a good accessory and a sad one usually comes down to what you can’t see in a photo. Metal hardware that’s actually plated properly, not just painted gold, so it doesn’t go patchy after a few weeks in your pocket. Stitching that’s tight and even, especially on anything with a buckle or a clasp, because that’s where things give way first. Leather, real or not, should have a bit of give to it rather than feeling like cardboard, and anything with elastic needs to still have some spring left after a wash, not just on day one in the shop. If you’re only going to spend properly on one thing, make it a belt or a decent scarf, because both get worn against your skin and both show up cheapness fast, the belt by curling at the edges, the scarf by bobbling the first time you wear a coat over it.
The pairing rules are simpler than people make them. A good leather belt will sit happily with almost anything that has a waistband, but it fights with anything already cinched or elasticated, you end up with two waistlines arguing with each other. Scarves want texture that matches rather than fights, so a chunky knit one looks wrong over something slippery and synthetic, it just slides about and looks accidental. Sunglasses are the one thing worth trying on properly rather than buying from a photo, because the frame that looks lovely on a narrow face can swallow a rounder one whole. Watches and hair clips are forgiving, they’ll go with most things, which is exactly why they’re the easiest to buy too many of.
Where accessories let you down is mostly about honesty with yourself over how roughly you actually live. A delicate clasp won’t survive a bag that gets thrown about, a pale fabric belt won’t survive white wine, and a hair clip with a weak spring will be in your coat pocket by lunchtime rather than in your hair. None of that means buy expensive, it means buy for what you’ll actually do in it, not what you’ll do in it once, for a photo.