I was recently talking to an independent "self-taught" Artist (who never attended Art School). She operates a Gallery/ Shop/ Class/ Studio space, and although this Artist had some obvious "talent" (talent being merely a combination of exposure, opportunity, practice and dedication), and keeping in mind her objective is to get students to her classes, I had a couple of issues with some of the statements she made.
I am also technically "untrained" which basically means I have not been to Art School. I learned some techniques in High School and during my studies in Interior Design, but before this (as a child) I made the art I wanted to make, because it was fun and nobody told me I was doing it "wrong".
I think Art School is a great shortcut to networking, using "art language" and learning how to use a medium. You have the benefit of other Artist's trials and tribulations at your fingertips. They introduce you to new materials and take some of the mistake-making out of learning how to create your work, and they introduce you to the Art of self-marketing...
This Artist implied that there is correct and incorrect technique.
She implied that everyone needs lessons (except herself) to reach their potential as an Artist.
She implied that YouTube videos sometimes teach you "wrong".
She implied that there is only one way to paint a tree.
Each Artist's work is a complex combination of their thoughts, experiences, emotions, materials and every single thing they have ever been exposed to. Our brains are like sponges absorbing everything around us. Each Artist's work is a combination of everything they have seen, heard, smelled, touched and felt. It is a mixture of styles from every Artist they admire and aspire to.
Who is one person to say someones technique is "wrong" because it doesn't match their own? If an Artist watches a YouTube video of another Artist painting and enjoys the finished product of the video (and hence tries to emulate or take some technique from the video), then how can the technique be "wrong"? What is right is only what is right for YOU.
Every Artist is on a journey of their own discovery and learning to make Art to suit another Artist is pointless and irrelevant.
There is no wrong answer.
Paint the tree however you want to paint it, and don't give up until it meets YOUR OWN expectations of what the tree should be.