The week everything else is in the wash, or the week you've got three different things on in three different places and no time to think about what goes with what, that's when black trousers actually prove themselves. Funerals, interviews, a school meeting straight after work, a dinner you forgot about until the afternoon. One pair, no decisions. That's the whole appeal, and it's a bigger deal than it sounds when your mornings are chaos.
A good pair earns that reputation slowly. The first few wears they sit a bit stiff round the waist and knee, then they soften and drop with you, which is why trying them on at the end of a long day rather than first thing tells you more about how they'll actually behave. Wash them inside out, cold, and skip the tumble dryer if you can bear to, because heat is what turns black to a dull, slightly purplish grey faster than anything else, and that's the thing that gives a cheap pair away months before the seams do. Hang them rather than fold them over a rail if you want to avoid a crease sitting permanently across the thigh. They're not, however, built for everything. A pair that's brilliant for sitting at a desk all day can be hopeless for anything that involves bending, crouching or getting in and out of a car repeatedly, so if your week is more on your feet than at a table, check the stretch before you check the colour. And a true matte black will do you no favours next to anything shiny or synthetic black, satin especially, because the mismatch in finish shows up under lights in a way that no amount of confidence fixes.
Fit is where most black trousers go wrong, and it's rarely the waist, it's the seat and the break at the ankle. Too much fabric pooling at the back reads as a size too big even when the waistband's snug, and too little gives you that pulled, strained look across the hip when you sit down. Try sitting in them in the changing room, not just standing side on to a mirror, because that's where a decent pair separates from a mediocre one. The hem matters more than people admit too, a half inch too long and they drag at the heel all day, catching under trainers or scuffing on pavements, a half inch too short and they look like they shrank in the wash even when they didn't.
Honestly, once you've found a pair that fits sitting down as well as standing up, you stop thinking about them at all, which is the highest compliment I can give any trousers.