Depreciation isn't based on realistic estimates. They're standards issued by a governing body to try and capture some expense of the reality of depreciation.
For example, there's not a Dodge minivan vs Honda minivan depreciation difference, even though, if you've had both, you know one depreciates much faster than the other.
In the example below, it says 5 years for furniture. Is all furniture worthless after 5 years? Of course not. There's an entire industry of centuries old antiques.
"Depreciation is a non-cash business expense that is allocated and calculated over the period that an asset is useful to your business."
