As a side note (not pointing fingers to anyone in particular, I just want to vent as I've been bit by this multiple times): I found that some raycasting tutorials are pretty bad and don't actually explain the math behind it.
I've been noticing this trend in tutorials to say "and now we have to use... MATH! ", and then proceed to go over it as fast as possible and just leave a code snippet - which sometimes is not even correct!
It's been really frustrating, because I know I have some issues with the projection (I think related to the FOV and not having a near plane), and it would be really useful to be able to double check my math once in a while.
And also, if I'm allowed extra ranty: I really don't get why someone would want to watch a tutorial that only explains the easy parts.