The advice that shoes need breaking in has caused more discarded footwear than almost any other belief in the category. Some things do change with wear, and the ones that matter mostly do not.
What genuinely changes
A short list.
Leather uppers soften and mould slightly to the foot over weeks. This is real and it is a modest change in flexibility rather than in size.
Soles flex more readily as they are worked, particularly stiff leather soles, which affects comfort in walking noticeably.
Insoles compress slightly, which effectively adds a small amount of volume.
And linings smooth where they contact the foot.
Together these produce a shoe that is somewhat more comfortable than when new, in the region of a small adjustment.
What does not change
The things people expect to and which determine fit.
Length. A shoe that is too short does not become longer.
Width across the widest part of the foot, which is set by the last the shoe was built on. Leather stretches slightly across the width and not by a size.
Heel fit. A heel that slips will continue to slip and generally gets worse as the counter softens.
Instep height, which is a structural dimension.
And the shape of the toe box relative to the shape of your toes, which is the most common source of persistent discomfort.
Why the belief persists
Two reasons, both understandable.
The genuine softening does produce improvement, so the advice is partly true, and people generalise from a real effect to an unlimited one.
And there is a strong reluctance to accept that an expensive purchase was wrong, which produces persistence past the point where the evidence is clear.
Retail also has an interest in the belief, since a customer who accepts that discomfort is temporary does not return the shoes.
What actually can be adjusted
By a cobbler rather than by wearing.
Stretching, which works on leather in specific areas — a bunion point, a width across the ball — and produces a genuine local increase.
Adding volume reducers or tongue pads, which addresses a shoe that is slightly too large.
Heel grips, which address slipping to a degree.
And insole changes, which adjust volume meaningfully.
None of these changes length, and a shoe of the wrong length cannot be corrected.
How to assess fit properly
The checks that would prevent most of the problem.
Try shoes late in the day, since feet swell measurably and a shoe fitted in the morning may be tight by evening.
Wear the socks you will actually wear with them.
Check the widest part of your foot sits at the widest part of the shoe, which is the single most useful check and which people rarely make.
Leave a small gap beyond the longest toe, which is not always the big toe.
Walk on a hard surface rather than on shop carpet, which flatters everything.
And measure both feet, since they commonly differ and the larger one determines the size.
The last
Worth understanding because it explains why some brands never fit you.
Shoes are built around a form called a last, which defines the internal shape.
Different makers use different lasts, and a maker's lasts tend to be consistent across their range.
Which means if one shoe from a maker fits well, others likely will, and if they consistently do not fit, no amount of size adjustment will help.
Identifying which makers suit your feet is more useful than any individual purchase decision.
The honest rule
A shoe should be comfortable in the shop, allowing for a modest improvement afterwards.
Discomfort at the point of purchase is a reason not to buy, not a temporary condition.
Pain anywhere is disqualifying, and the belief that it will resolve is the specific error that this whole piece exists to address.
Sizing across regions
A practical complication for anybody buying internationally.
Shoe sizing systems differ between regions and the conversion charts are approximate, since the underlying systems measure different things.
Width designations differ even more, with several incompatible schemes in use.
Which means a conversion is a starting point rather than an answer, and buying an unfamiliar brand from another market without trying it carries real risk.
Measuring your foot in centimetres and using the manufacturer's own chart is more reliable than any general conversion.
The return window
The practical protection against getting this wrong.
Wearing shoes indoors on a clean surface for a few hours, over several days, reveals nearly every fit problem while leaving them returnable.
Most retailers accept returns on shoes worn only indoors and unmarked, and checking that policy before buying is worth doing.
This is by some distance the most reliable method of avoiding an expensive mistake, and it is available to anybody who resists the urge to wear them out immediately.