Hi,

"If you have 5 apples in your inventory and sell 10, before having done the delivery, you get: - forecasted quantities: -5 - on hand quantities: +5 It's of course impossible that, in the future, you get "-5" apple in your inventory. But it's a great information since it tells you that if you do nothing, you will be 5 apples short according to what you promised to your customers. In real life, if your inventory is correct, you will deliver 5 apples to your customer and keep the others 5 in a backorder. But if, in real life, you force the system and deliver 10, Odoo lets you do it instead of blocking the delivery order operation."

Please see the rest of the answer provided by the Fabien here: https://www.odoo.com/forum/help-1/question/negative-on-hand-should-be-physically-impossible-59608

Thanks