The moment indigo jeans properly clicked for me was a plain white shirt, tucked in, sleeves pushed up, with a dark pair that still had that slightly stiff, inky feel to them, worn with nothing else trying to compete. No jewellery, flat boots, out the door in four minutes flat. It wasn't a complicated outfit. That was the point. The dark wash did all the work that a print or a cut usually has to do, and I remember thinking, oh, so this is why people go on about them.
Where they stop being the answer is anywhere you need softness or movement straight out of the packet, a long train journey, a day on your feet, anything where you want give before the denim's had a chance to relax into you. A proper indigo pair with any decent weight to it will feel like you're breaking in a new bag for the first couple of wears, a bit stiff at the knee and waistband, and if you buy them a size up hoping that'll fix it, you'll just end up with jeans that bag at the back by lunchtime instead of looking sharp. They soften properly over a few months of normal wear, the fade starts along the fold lines and the seat if you're sitting a lot, and that's the bit that actually looks good, a worn in colour that's gone slightly grey blue rather than the flat new dye. Wash them inside out, cold, as little as you can get away with, and hang rather than tumble, because heat is what kills that colour fastest and turns a deep indigo patchy in a way no amount of ironing fixes. A cheap pair will crock, meaning the dye rubs off onto your hands, your sofa, anything pale you lean against, which is a genuinely annoying way to find out you bought the wrong ones.
The difference between a good pair and a disappointing one shows up at the seams and the hardware before it shows up anywhere else. Run your thumb along the inseam, it should feel flat and tight, not puckered. A proper metal button with some actual weight, rivets that sit flush rather than poking, a fly that doesn't gape when you sit down. Cheap denim feels thin and slightly papery even when it's dark, and no wash will ever disguise that.
The one mistake worth avoiding is judging the colour under shop lighting and then being shocked at how blue they look by a window at home. Check them in daylight before you commit.