[mothered]

Because there is 4 things they cant know exact weight of something, just going to say it was missing.

They do know.

Whether there's four Items or forty, Is Immaterial. Here's a hypothetical scenario.

*The package weighed 2Kg when you received It.
* You claimed an Item (with a significant weight) was missing.
* They deduct the Item's weight off the total consignment.
* They cross-check this, against the weight of the package that was dispatched & received, which was 2Kg.
* A mismatch In weight, means the Item could not have been missing when received.