Now, sometimes the situation may not be in your control such as shipping delays while the order is in transit, but you still need to understand the situation from your customer's perspective.
Not everyone is aware that the situation is out of your hands, and sometimes people tend to confuse shipment with Amazon-like services where Amazon takes care of shipping too.
I've heard people calling customers "stupid" and not care much at this point, but try to think what it's like being in their shoes. Just like not everyone is tech-savvy.