What is the best (paid or free) grasshopper tutorial/book/course or other way to learn grasshopper in 2018? (self.rhino)

I have been doing the grasshopper tutorials on t, but quite a few of them are a little outdated (for instance, some require T-splines, which is not available anymore). I also found some of the tutorials lacking in the sense that they often don’t explain why they’re doing things in a certain way, you just follow along and eventually something cool pops out.

Is there a really good book or course or set of tutorials that teach you Grasshopper really well?

But mostly if you really want to learn, struggle through some other peoples problems on this forum. Trial and error, just go for it.