When an item comes in from a truck it either goes directly onto the sales floor, into overstock (a high shelf above the other items), or into the backroom. People put things back in random places, stuff get destroyed (think of dropping a can on the ground), stuff get stollen, cashiers make a mistake, people make a mistake in self checkout, probably other stuff I am missing. It is a store, things are chaotic.
Let's take the journey of some cans of Goya black beans. 12 come in on a truck. The shelf capacity for them is 4. The person unloading the truck takes beans to the sales-floor, puts 4 on the shelf, puts 4 into overstock puts 4 into the backroom. Joe walks in takes a can, drops it and it bends. Jane comes along takes a can, continues shopping, the changes her mind and leaves it somewhere in the cereal aisle. Janet comes along and takes a can, takes it to self checkout but forgets to scan it. Jacob comes along takes a can, takes it to the checkout, and 1 can is subtracted from inventory. Inventory shows 11 cans, but there are actually 0 cans out on the sales floor. And I haven't even gotten into stuff being misplaced in the backroom ect.
Let's take the journey of some cans of Goya black beans. 12 come in on a truck. The shelf capacity for them is 4. The person unloading the truck takes beans to the sales-floor, puts 4 on the shelf, puts 4 into overstock puts 4 into the backroom. Joe walks in takes a can, drops it and it bends. Jane comes along takes a can, continues shopping, the changes her mind and leaves it somewhere in the cereal aisle. Janet comes along and takes a can, takes it to self checkout but forgets to scan it. Jacob comes along takes a can, takes it to the checkout, and 1 can is subtracted from inventory. Inventory shows 11 cans, but there are actually 0 cans out on the sales floor. And I haven't even gotten into stuff being misplaced in the backroom ect.