The moment it clicked was on a packed train platform, trying to find my travel card in a tote bag with lining the colour of wet tarmac, holding up the queue while a man behind me sighed audibly. A friend standing next to me just tipped her mesh bag towards the light and pointed. Card, keys, lipstick, all visible, all findable in about two seconds. I bought one the following week out of sheer embarrassment and it has not left my side since, mostly for a beach trip to Portobello where sand fell straight through the holes instead of living in the bottom seam for a fortnight.
If you've never owned one, start with a mid sized structured mesh tote in a firm nylon or coated cotton mesh rather than the floppy string versions, because the stiffer weave holds its shape on your shoulder instead of collapsing into a bag shaped puddle the second you put anything heavy in it. A firm base and a zip or clasp top matter more than colour at this stage, since an open mesh bag with no closure means your phone is basically on public display on the bus. Go for black or navy first if you want it to behave like a normal bag on an ordinary Tuesday, and save the clear vinyl mesh or the neon nylon ones for when you've decided you actually like the honesty of the thing.
It sits oddly well against things you'd think would clash with it. Denim, obviously, but also linen trousers and a plain cotton shirt, because the mesh adds texture without adding colour, so it doesn't fight with a print the way a patterned bag would. I've worn mine with a grey knit dress and trainers and it looked considered rather than accidental, which surprised me, given it's essentially a bag made of holes.
Seasonally it belongs to warmer months, spring through early autumn, and to anything outdoorsy or chaotic: markets, festivals, beach days, picnics where sand and crumbs need somewhere to fall that isn't your actual belongings. It's a poor choice for anything you need kept dry or private, so leave it at home for winter and for any day you're carrying paperwork you don't want the whole bus to see.
It suits anyone who's tired of digging through a dark bag for their keys and doesn't mind the whole world watching them do it instead.