system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why is it so hard to reverse-engineer something? Shouldn't it be simple to just copy the parts exactly?
gpt
No.

Let's say you try and reverse engineer an iPhone. 

You need to know what each component is made of, this is NOT easy at all and requires some fairly high level analytical skills. 

You also need to know how each component talks to each other. An iPhone isn't just the solid stuff, and then OS installed; there is firmware that controls how say the capacitance from the screen is delivered to other bits of circuitry. There is software that controls the battery.

Another example would be say a grain mill! You could build something that looks the same easily; a stone with an axel and then another stone on a pivot that can roll along in a circle. But if you don't know how to use it (the software) it's useless. 

With modern stuff the material becomes a big factor!! Touch screens are made of very special materials for one. Military hardware? Can also be very exotic composites, it's not just steel etc.