Sounds easy when I say it like that, but it’s not 
getting the right amount and balance of nutrients is what I find hard.
Plants will get a deficiency, in one thing, so you add more, but most of the time you are guessing how much, and how fast the bacteria are working, so it’s easy to screw up and throw the whole system out of whack, adding too much of one thing.
With bottled nutrients you know exactly what is going in, what your ph/EC is, all they have to do is guess how much the plant can handle before it burns. Organic is kinda like driving blindfolded and someone telling you left or right on the steering wheel lol.
When you buy these JAW soils you trust that everything in the bag is as advertised but there will always be descrepences, and to know properly, you have to have it tested at some cost, to know exactly what you have at the start, in order to know how much to replace when it depletes. To understand the tiny details of a plants expression of when it needs or doesn’t need something takes a lot of time and experience, to act just before it becomes a problem.
When it’s going well it’s a breeze to grow good weed, but when it’s out of whack it’s a pain on the ass, and frustrates the hell out of me, because there is so much more to learn, to keep it consistent. It’s also why I love it as it’s the challenge I enjoy the most. I would still grow even if I didn’t use it anymore.