Sometimes supply, sometimes demand.

Certain items are invented before there is a great demand for them. EX: a piano.

Other items are created because there is a great demand already. EX: the automobile.

I can tell you it is one of the 4 items: product demand, derived demand, resource utilization, or cost minimization

It probably depends on how much of a demand there is for the product. If the demand is high for a product, that means they probably have a surplus of it and will accept an order of ten items. However, if there is a small demand, they probably do not have many and will not accept a large order.

An independent demand is a demand that is not based on the demand for another item while a dependent demand is based on the demand for another item.

For example, the demand for chairs of a table and the table itself is based on the demand for the table. The table in this example is the item with independent demand. Knowing this, one can forecast an independent demand while dependent demands are calculated based on the independent demand item. Business to business independent demands tend to be demands for such items as capital goods, office supplies, MRO (maintenance, repair, and operating) items, and anything else for which the dependency is unknown. Independent demands are usually handled with standalone purchase orders, although some items might be covered by contractual relationships such as volume, price and other agreements.

because demand exceeded supply.