I am a hobbyist photographer, and everything in photography pretty much falls under the exposure triangle when you get technical. You can teach adding 1 stop of light by subtracting it from another area (ISO, aperture, and shutter speed). It's kind of difficult to teach that if you take 1 ISO away, you need to add it to open up the aperture or slow down the shutter speed to get the same result. It gets frustrating, so I was never really able to teach that. Also, photography is pretty subjective in the way you take a photo and how you frame it, such as the 2/3rds method. There is so much involved in that, technically and subjectively, it makes it difficult to teach someone, in my opinion.
But, give me a person who doesn't know how to shoot, and by the end of the day, I will have them in the black every single shot. It's not that technical to teach someone to breathe, brace, relax, etc.
The way I can teach someone to shoot, I can teach them to properly lift (exercise) too.
Re-reading this, it seems like all 3 could be teachable, but I just find it easier working with someone's body and physically adjusting it to make proper corrections over the very technical stuff photography adds to the table.