It clicked for me on a Tuesday when I'd worn the same navy pair to a lunch and then straight to the sort of casual drinks where you're stood at a high table for two hours. No change needed, no tights to fuss with, just a different top and different shoes and suddenly I looked like I'd made an effort both times. That's the whole point of a cropped trouser, really. It's the trick of looking finished without looking like you tried.
Getting the length right is the entire game here, and it's where most people, me included, go wrong at least once. You want the hem hitting somewhere between the slimmest part of your ankle and a couple of inches above it, not mid calf, which flatters almost nobody and just reads as trousers that shrank in the wash. Go barefoot or in the heel height you'll actually wear them with when you try a pair on, because an inch of difference changes everything. Watch the waist too, since cropped styles often sit higher to balance the shorter leg, and if there's no give at all through the hip you'll feel it within the hour, not after a big lunch. Where they properly fall apart is anything that needs real stretch or bending low, gardening, a long train journey where you want to curl your legs up, a day that's mostly sitting on the floor with a toddler. I kept a linen pair for a summer of exactly that and they went baggy at the knee by the second wear and never recovered. They're also not the move if you're after warmth, obviously, the ankle's exposed and no amount of styling fixes that in February.
The difference between a pair that lasts and one that's bin material by autumn is almost always in the fabric weight and the finish at the hem. Cheap cotton goes thin and shiny at the knee within a season, and a raw or unfinished hem that looked deliberate in the shop will fray properly after three washes, not elegantly. Look for a proper turned hem with a bit of stitching weight to it, and a fabric with some structure, a cotton twill or a wool blend holds its shape through a bag squash far better than anything floaty. Zips and buttons matter more than you'd guess on a trouser you're taking on and off all day, a flimsy zip pull snaps within weeks of actual wear, especially if you're one to yank it.
If you're between sizes, size for the waist and hip and get the length taken up properly rather than buying a size down to shorten the leg.