There is a scene that repeats itself. You take a photo to the salon, you come out with that cut technically well executed, you look in the mirror and something does not add up. You could not say what. The cut is the same. The face is not.
This is not bad luck, and it is not that "nothing suits you". It is that a haircut is not an object that looks good or bad on its own, it is an intervention on a specific set of proportions.
What does a haircut actually do?
Four things, and almost every decision can be explained with them.
It adds or removes width at the height where it ends. A cut finishing at jaw level puts volume right there, and therefore widens right there.
It lengthens or shortens the face. Lengths falling below the jaw stretch the vertical. Lengths ending above it cut the vertical short.
It lifts or lowers visual weight. Volume at the crown raises attention. Volume at the sides spreads it sideways.
It steers the gaze. A side parting introduces a diagonal. A centre parting marks symmetry and the vertical.
None of the four is good or bad. They are effects. Whether they suit you depends on what your face needs.
Why does the same cut not work the same on two people?
Because the effect is the same but the starting point is not.
A bob at jaw level adds width there. On a long face that tends to be exactly what was missing, because it gives width back where there is excess length. On a round face, that same bob adds width where there was already width, and that is why it tends to round things further.
The cut did not change. The face did.
That is the whole matter, and it is also why lists of "the cuts everyone is wearing this season" are of little use. They describe the cut, not the effect.
Orientation by shape
Before the list, a warning: these are tendencies that work most of the time, not rules. Your hair texture, its density and how much time you are willing to give it each morning weigh as much as the geometry.
Round face. Tends to welcome lengths that pass the jaw and volume in the upper part. Layers starting below the chin tend to lengthen. Lengths ending exactly at jaw level tend to widen.
Square face. The jaw is the strong feature. Soft waves and layers falling around the oval usually soften the horizontal without hiding it. Very blunt cuts at the angle of the jaw tend to underline it.
Rectangular or long face. Here width is usually what is missing, not length. Volume at the sides and a fringe are the two resources that balance most. Very straight, unlayered lengths tend to stretch things further.
Heart face. Wide forehead, narrow chin. Lengths with volume at jaw level tend to compensate for that difference. Volume concentrated on top usually accentuates it.
Diamond face. The cheekbones lead. What tends to work is giving some width at forehead and jaw to spread things out, with fringes and lengths that do not cling to the cheekbone area.
Triangle face. The jaw is wider than the forehead. Volume in the upper part usually rebalances, and lengths that accumulate weight low down tend to load the area that already carries weight.
Oval face. Takes almost everything, which is a blessing and a trap at once. When there is nothing to compensate for, the decision stops being geometric and becomes one of character.
And if you already cut something that does not suit you?
It happens, and it is less serious than it feels in the moment. Almost everything can be corrected without scissors: the parting, the volume, the direction of the blow-dry and even where you tie your hair up change the effect considerably.
An example that tends to surprise people. If you have a bob that widens your face, moving the parting from centre to side introduces a diagonal and corrects a good part of the problem. There is no need to wait six months.
The order that avoids most mistakes
Structure first, cut second. Not the other way round.
When you know what your face does, you stop asking "will this suit me?" and start asking "does this add width or remove it, and which do I need?". That is a question you can actually answer before sitting in the chair.
And it has a side effect I find the most valuable of all: you can explain to whoever cuts your hair what you are after in terms of effect rather than reference. It changes the conversation considerably.
Start with your shape
The face diagnosis works it out by measuring four distances, not by comparing you to drawings. You fill it in on screen, download it, and no sign-up is needed.
Then the guide for your shape covers the cuts that suit it and the ones that work against it, with the reasoning behind each, plus fringes, hairstyles, hair accessories, earrings and necklaces: the seven guides.