I had a moment in Tunic where I realized what the references in the manual to the [HOLY CROSS] were talking about, but I don't think my revelation was the typical.
I'd actually figured out the [HOLY CROSS] really early on, solved a bunch of puzzles using it, got some manual pages I probably wasn't supposed to have yet, but didn't know that the thing I was using was the [HOLY CROSS] because I lacked the context of a certain page that spells it out and based on some comments and videos elsewhere is the point where a lot of people first figure out how to use it.
It probably didn't hurt that I was fresh off The Witness and my brain was subconsciously looking for tricks of perspective and environmental puzzles, which Tunic is absolutely full of.