Like others said, you sort of can. But I also want to add that things like functions names, or comments explaining how a function works, are not needed by your computer when running the program, and thus they get lost after compiling. After running a program designed to reverse engineer a compiled program, you'll be able to see a very dumbed down version; no meaningful function or variable names nor comments explaining the code. You have to figure those out all by yourself.

And add to that that some companies/programmers make some parts of the program difficult to read on purpose, so you have more guesswork to do when reverse engineering, and you've got a giant task ahead of you reverse engineering even small games.

On a side note, the original source code can also just be interesting or funny to read. Valve's source code comments come to mind.