As someone who has grown for a long time, I would have to say the most limiting factor for me would be my lack of proper documentation. It is damn near impossible to properly asses a situation without all of the pertinent information. I can tell myself the same thing every year "im going to write down everything", then lo and behold , I'm halfway through another grow and I have a couple of things scrawled down on the back of a waterlogged pop tart box, and a handful of receipts from the local gardening store stuffed into an old peat pot that has been sitting in the same spot since I cut my finger trying to separate the damn thing from its siamese twin and had to go find a band-aid.
All joking aside, if I had to pick one thing that i think holds me back from being a REALLY GOOD grower that would be the one. Im 56 years old and have been growing since I was in my early twenties, with some time off for family and career and such, ive done indoor/ outdoor hydro and organic, and without the notes I would have been starting over every year. When we attempt to solve a problem the first thing we do is ask for information, and without those answers often we are lost, so yes proper documentation is key for me.