As a developer, you should never assume you understand how something works solely by observing what it does. This is especially true if you are trying to fix something and your only understanding of the issue is only the behavior that you can observe.
While you don’t have to understand how something works in order to use it, if you’re trying to fix something, especially software, it helps to understand how something works. The reason is what you observe externally as a problem is usually only a symptom of the problem; it’s rarely the actual problem itself.
Let me give you an extremely simplified example. Let’s say you have an electric car, but you’ve no idea how the electric motor drivetrain works, you just know you press the accelerator pedal and it goes. One morning you get in the car and press the pedal and nothing happens. In diagnosing the issue, the only thing you consider is the external symptoms that you can see: you press the pedal and it doesn’t go. An extremely naive conclusion you could make is that the accelerator pedal is broken (!). So you replace the pedal, but then you’re surprised to find that it still doesn’t work (ok, so this is a contrived example to make the point – if you know enough to be able to replace the accelerator pedal, you probably know enough about how the car works to not assume the pedal is broken!)
As a software developer or architect, as you diagnose issues you should always look under the covers and find out more about what’s actually going on. The problem you’re looking for is rarely the symptom that you can actually see (or what the user sees).