Every shoe is built around a last, a solid form standing in for the foot. Almost everything about how a shoe fits and looks is decided when that form is chosen.
The last is a shape, not a size
A last is a three-dimensional block, made in wood or plastic, over which the upper is stretched and to which the sole is attached.
It is not a copy of a foot. It exaggerates and reduces in specific places to produce the silhouette the maker wants while still accommodating the wearer.
A maker will keep a small number of lasts and produce many models from each, which is why shoes from one house often fit consistently across very different styles.
Fit is set by volume, not by length
Two lasts of the same length can differ substantially in instep height, width across the ball and heel cup dimensions.
That internal volume determines whether a foot is held or squeezed, and it is why a person can take one size in one brand and a different one elsewhere.
Shops that fit properly ask about width and instep because those are the dimensions the last controls and that the printed size never mentions.
Toe shape is a proportion decision
A chisel, almond or round toe is a property of the last, decided before any pattern is cut for the upper.
Longer, more tapered lasts create elegance by extending the shoe beyond the toes, which is why a formal shoe often looks larger than a casual one in the same size.
That extension has a limit. Push it too far and the ball of the foot no longer sits where the last is widest, and the shoe becomes uncomfortable regardless of length.
Lasting is where the upper takes its final shape
Leather is dampened and pulled tight over the last, then secured while it dries, so it holds the form permanently once released.
Time on the last matters. Leaving a shoe lasted for longer allows the material to settle into the shape rather than fighting to return, which is one difference between hurried and unhurried production.
Removing the last too early is a common cause of shoes that lose their line quickly and wrinkle across the vamp in odd places.
Sneaker lasts follow different constraints
Athletic lasts are usually straighter and more voluminous, since the foot swells during activity and needs room the dress shoe does not have to provide.
Many are built for cemented or injection-moulded construction rather than stitching, which changes how the upper is pulled and where it is anchored.
The underlying principle is unchanged. The last defines the internal space and the external line, and no amount of cushioning added afterwards corrects a form that does not suit the foot.