Have you ever noticed no one seems to get tutorials right? They either give you not enough information, or they try to make it like the game. Ok space pilot, press the d key now. Doesn't work. I just want to be given a list of keys or controls and try them out in simulation where I won't get killed right away and then get on with the game.
Yes, I often find that the code they post ONLY works in very particular circumstances.
A common one is shadows, you test their code and it works then drop it into your own code and it doesn't .
They just don't tell you that the bias is SOOOOO important and often needs to be hand tweaked for each scene.