That we learn through failure is, of course, well known. We can also learn from other people's failures as well. "So what?!" I hear you say. Well, let me give you a practical example of the principle at work.
I was asked to stain and varnish some tables. Staining is a little tricky. It requires the stain to be brushed on evenly, then quickly wiped off while still wet. If not, it will leave an uneven colour across the wood. To help me understand, we watched a Youtube video of an expert craftsman explaining how to apply stain while casually staining a counter top. Easy! Just follow the instructions and do what he did. Except, of course, all the issues we encountered that were never mentioned by the expert. Needless to say, the staining turned out terrible!
If you want to learn a skill via Youtube (or any other means that does not involve personal interaction with the expert) do not watch the best person who does it - the expert, master craftsman, trained professional, or the "si fu". Watch the worst person - the hobbyist, the beginner, the "kid", the learner. They fail, and you can learn from their mistakes. How can you tell the best from the worst? If you watch them and can think to yourself, "That's easy! I could do that", stop the video and find someone else!
PS. I am not knocking experts - I love to watch them at work and marvel at their skills. I just know this is the level to achive, not a lesson to get there. Some experts not to watch (:-p): Jimmy Diresta (building stuff), Clickspring (mesmerising clockmaking), Bosnian Bill (Lock picking), Izzy Swan and Get Hands Dirty (Carpentry) and Primitive Technology (survival?), Vsauce (Education)