It's not enough to just identify your mistakes (quiescence errors, lack of visualization, Hope Chess, hand-waving, misapplying principles, lack of recognition of basic tactic patterns...). You want to identify causes & take strong steps that minimize similar mistakes in the future. Otherwise your playing strength is stuck.
My job as an instructor is to help you do those things. Sure, most of the work will be yours, but my job is to identify the areas of need and improvement and put you on the right track. To improve you need practice, study, and feedback. Without the dimension of feedback you get diminishing returns on your study and play.
Dan Heisman is a USCF Master, full-time instructor, and author of 12 chess books and an extensive Youtube Channel.