If you are stood there holding one, unsure, here is what I would say. A trench works harder than almost anything else you could buy this month, because it covers a suit, a jumper and jeans, and a dress you are not sure about, and makes all three look like you planned them. Buy it a size that lets the belt actually do something, not one so fitted you can only wear it open.
It is not the answer to everything though. In proper heavy rain, a lot of them let you down, because the classic cotton gabardine is showerproof rather than waterproof, and you will find that out on the one day you really needed it not to be. It is also not built for deep cold on its own, so if you are stood at a bus stop in January with nothing underneath, you will be cold and smart looking at the same time, which is not much comfort. Treat it as the layer that goes over a proper coat's worth of warmth, not instead of it.
It clashes with fuss. A lot of print, a statement bag, chunky jewellery and a trench on top starts to look like you got dressed twice. It sits best over something plain, a crew neck jumper, straight jeans, flat boots, or a simple dress and tights, and it lets the shape of the coat and the belt be the whole outfit. I would also leave it at home with anything already quite tailored and stiff, two structured pieces fighting each other never looks deliberate.
Worn properly, a good trench gets better with time rather than worse. The cotton softens slightly, the collar relaxes, and it starts to crease in the places you actually move, which looks lived in rather than scruffy. Hang it on a proper hanger rather than scrunching it on a hook, do the belt up loosely when it is not on you so it does not crease in one spot forever, and only dry clean when it genuinely needs it, because that treatment over years is what eventually makes the fabric go thin and papery.
The difference between one that lasts and one that disappoints is mostly in the details you only notice once you own it. Buttons that feel like actual horn or proper resin rather than thin plastic that scratches. A belt with a solid buckle, not one that slips and leaves you retying it on the walk to the station. Proper stitching on the storm flap across the shoulder, and enough weight in the cotton that it hangs rather than flaps about in the wind. Cheap versions look nearly identical on a hanger and then crease in the wrong places after one wear.
Reach for it on the days that sit between seasons, when a heavy coat is too much and nothing else feels finished, and on the mornings you have not decided what you are, because it decides it for you.
Picked by Lauren Booth. More in Coats.