When a customer asks for a size 42 and you are not sure if you have it, you have already lost something. Not the sale — the clarity about what you actually own.
You go to the shelf. You check the stock room. You call out to your staff. Sometimes the size is there. Sometimes it was sold three days ago and nobody updated anything. The customer waits. You look uncertain. Even if the size is there, you have already spent more time on one question than the sale is worth.
This is the size problem. It is not about having the wrong stock. It is about not knowing what you have.
Shoe retail is inventory-dense in a specific way. One style across five sizes is five separate items that move at different rates. A size 40 might sell in a week. A size 45 might sit for two months. A notebook cannot capture this without someone counting every size on every shelf and writing it down correctly every day. Nobody does that.
What actually happens is that the notebook records sales as they happen, but stock levels are reconstructed from memory and occasional physical counts. The gap between what the notebook says and what is actually on the shelf grows over time — faster in busy periods, slower in slow ones, but always in one direction.
A system that tracks sales by size closes this gap automatically. Every sale removes one unit from the right size. The restock list that comes out at the end of the week reflects what actually moved, not what someone remembers moving. You walk into your supplier knowing you need four pairs of size 41 and two of size 43, not a rough estimate based on what felt busy.
The size problem is not about the sizes. It is about having current information at the point when it matters — when a customer is standing in front of you, or when you are placing an order. The notebook cannot give you that. The count on the shelf can, but only if someone just counted it. A live system can, any time you look.