This is also one of my favorite things about open source software. I can view the source to understand what's causing a bug, to fill in knowledge gaps left by the documentation, or just learn more about programming concepts. Nothing is hidden.
On the contrary, you don't need the source, and in some cases it may even be misleading in many ways, when you can look directly at the instructions the machine executes. Tools like disassemblers and decompilers would be equivalent to what you speak of.
Nothing stops you from doing this with open source software either, though; making something open source is strictly an increase in the information available, and at least to me that seems in the spirit of "show me things that are normally hidden"
On the contrary, you don't need the source, and in some cases it may even be misleading in many ways, when you can look directly at the instructions the machine executes. Tools like disassemblers and decompilers would be equivalent to what you speak of.