Many years ago I got some very good advice from my college ski instructor -- "Go ski and when you reach a plateau or have some trouble, go take a lesson, get it fixed and then go ski some more." I firmly believe this is also true for Scuba.
Unfortunately too many people think they can only take a class to deal with an issue. (Maybe that's because there are so many "specialty" classes.)
About year ago I was very fortunate to hook up with an instructor who we (there were three of us) hired for a weekend of diving. He very quickly identified significant issues for all of us and then helped each of us work on those issues. Just as with my skiing, my diving skills improved significantly. (Full disclosure, we liked what he did so much we rescheduled for another weekend and then another over a several month period -- and even though it had not started out as a class, by the end of the 3rd weekend he decided that he had taught us a complete class and "gave" us the cards.)
Sometimes you NEED an instructor (a GOOD instructor) to help you over a hump. (Also full disclosure, the mentor TSandM referred to was (and is) a very good instructor who just happened to decide TSandM was going to be a freebie project for him.)