I spent years treating black t-shirts as the thing you buy without thinking, four in a pack, done. What changed was washing one for the first time and watching it come out looking like it had been left in a car boot over a Cornish winter, all patchy and grey at the hems, and realising the cheap ones had been quietly ruining my mood for a decade without my noticing.
A decent black tee is the thing that makes everything else in your wardrobe look like you tried. Under a blazer it reads smart without effort, tucked into jeans it reads like you got dressed on purpose rather than by accident, and layered under a shirt left open it stops a whole outfit looking unfinished. It takes gold jewellery, it takes silver, it doesn't argue with either, which is more than I can say for most colours. Worn with a slip skirt and boots it does an evening, worn with joggers it does a Tuesday, and nobody clocks that it's the same top doing both jobs because black has a way of looking deliberate even when it absolutely wasn't.
What nobody tells you is how fast a bad one gives itself away. Cheap cotton goes thin under the arms within a month, pills along anywhere a bag strap sits, and fades to that flat charcoal that photographs fine but looks tired in daylight. Turn it inside out before washing, keep it out of the tumble dryer, and a good one will still be properly black, not greyish black, six months in. That's the whole test, really, not how it looks on day one but how it looks after fifteen washes, which is not a test the shop mirror can ever show you.
Fit is where most of them fall apart in a different way. Too boxy and it reads like sleepwear, too fitted and it clings in a way that stretches thin over the chest and goes faintly see through under shop lighting, which nobody discovers until they're standing somewhere with bad lighting and good company. Check the shoulder seam sits where your actual shoulder ends rather than halfway down your arm, check the armhole doesn't gape when you lift a cup, and check the length doesn't ride up the second you sit down, because a t-shirt that needs constant tugging back into place isn't doing its one job.
Next time you're holding one up, skip the front entirely and hold it up to the light first, that's where the cheap fabric gives itself away before you've even tried it on.