Tuesday, 8.12am. You put on the jacket that looked so good in the bedroom mirror. By 7pm, after an hour in a café chair, you catch your reflection in the window: the back has turned into a road map, one shoulder is pulling, and the lining is rustling like a plastic bag. The piece hasn't changed — the day has passed judgment on it.

A piece that has to work from morning to evening can't just look good when you're standing up. It has to survive the chair, office lighting, the coat you take off and a dinner that starts late. So how can you tell before you get to the till? Sit down. Walk about. What happens when you're seated often tells you more than the fitting-room mirror.

The sitting test

Here's the fitting-room test nobody does: sit down. Not for three seconds, and not while holding your breath — stay seated a few minutes, ideally long enough for the fabric to relax. In the changing room or at home, with the jacket done up, the trousers bunched at the lap and your phone in the pocket. Like a day at the office, basically. If you have to stand up to check the state of the fabric, that's already an answer.

A woman sitting on a fitting-room bench, jacket done up, looking at the creases marking her legs
Jacket done up, phone in pocket: sitting down tests the piece better than a mirror

What are you looking for? Deep creases behind the thighs, a knee that keeps the mark, a shoulder that rides up. Natural, slightly structured fabrics — wool, dense cotton, a linen blend — often recover more elegantly than very soft ones. Just check the synthetic fibre content on the label: useful information, not a damning verdict. A piece that creases when you sit should recover without drama, not sentence you to a blanket over your knees.

The three-mirror method: look at the piece from the front, from the back, then seated. If the back worries you, wear it for an evening before you cut the label off. Dinner lighting shows up what changing-room lighting hides.

Drape has to be seen in motion

In a changing room, it's tempting to strike a pose. But life isn't lived standing still. Take three steps, sit down, stand up, reach for a folder or a glass. That's where the drape shows: does the fabric fall with you, or does it stay behind, having its own conversation?

A woman in a blue suit walking in a changing room, arm outstretched, to judge how the fabric drapes
Three steps and an outstretched arm: drape is judged in motion

A good wardrobe piece shouldn't be a sculpture. If the fabric creases across the back, leaves a mark under the knee or concertinas the moment you sit down, you know what Monday has in store. A slightly denser fabric, on the other hand, can look severe on the hanger and prove surprisingly elegant in motion. A highly structured piece flatters some silhouettes and weighs down others; the sitting test settles the question faster than any talk of cut. The mirror lies a little; walking lies much less.

One jacket, two lives

A work jacket that can go on to dinner isn't necessarily an evening jacket. It's a piece that will take a change of accessories: a fine roll-neck in the morning, a silk top at night, flat ankle boots and then heels. Layering is your friend, as long as it doesn't turn your silhouette into a layer cake. One fine layer under a well-cut piece beats three layers pulling at the shoulders.

A woman adjusting a camel blazer worn over a fine silk roll-neck
Fine roll-neck in the morning, silk top at night: one jacket, two lives

The alterations budget

With an almost perfect piece, an alteration can make the difference: taking in the lining, shortening a hem, nipping in the waist slightly. At a local tailor's or dry cleaner's, expect to pay roughly £10 to £25 for a simple hem, and more like £25 to £50 to rework a lining. Prices vary by city, fabric and complexity — always ask for a quote first.

In the end, the perfect piece isn't the one that follows you everywhere: it's the one that holds up through your day without asking you to play the statue. So next time, before you say yes to a lovely promise in the mirror, sit down and walk about. Your 8pm dinner will thank you.