As a Buddhist, I do not like bragging. (That would violate one of the Precepts or formal vows that I took as a layman or upasaka.) But neither do I like false modesty. I prefer simple, objective statements of fact.
So in response to today's question, I have to say that I don't believe I ever made any "mistakes" in my literary career, partly because something I don't have is a "careerist" attitude toward writing. I write prodigiously, but I have no image of myself as a "writer." I don't conceptualize myself that way. As I've said a million times, being a "writer" was not my chosen profession. In my youth, I was a professional cartoonist/illustrator, journalist, and passionate student of philosophy. So I've always had a certain psychic distance from the activity of writing. And especially from the "book world." My ego isn't tied up in it. But once it became clear to me in the early 1970s that it was my personal duty (given my background) to create certain works to enrich American literature, I carefully studied the lives and works of American writers before me, especially the black ones, in order to learn from their mistakes. I did the same thing with John Gardner, who was arguably the best teacher of creative writing in our time. In high school, college, and graduate school I studied then later taught American (and world) literature to determine what was not there, what I felt needed to be there (a vigorous interface between philosophy Eastern and Western and fiction, and a respectful portrayal of the life of the spirit), then I worked steadily, systematically, year in year out, for 40 years to fill those gaps, and stretch those intellectual and aesthetic boundaries.
For the specific kind of writer I am---a philosophical one---I think I prepared myself fully. In other words, earning the Ph.D. in philosophy gave me the credentials I needed as a Western philosopher. I was tested and retested at two schools on Western intellectual history from the pre-Socratics to 20th century thinkers, and had to accumulate over time competency in Spanish, reading French and, on my own for the past 13 years, some facility with Sanskrit and Pali. I studied all 20th century methodological approaches in philosophy and immersed myself in one: phenomenology. I also worked harder than many of my fellow students in philosophy by, for example, studying philosophical works that were not required for the doctorate. Not taught by the faculty during my time in graduate school. So, for example, when I write about my passion, Eastern philosophy, I do so with Western rigor, not in the fuzzy-wuzzy, touchy-feely way that characterized too much popular writing about the East in the 1960s and early '70s.
And I think the artistic and intellectual range and depth of my body of work has no parallel in American literature. Certainly not in black American literature. As Dr. Richard Hart writes in "Charles Johnson: Philosopher, Writer, Friend" in Charles Johnson: Embracing the World, "A challenge to any possible skeptic---do a serious read and re-read of any handful of Johnson stories, think about them deeply, and then, after careful reflection, tell us who does it better? Who has a richer, more complex network of ideas and concepts and arguments permeating every page of the text? Who does a better job of making his reader think about the toughest, perennial questions of life and its meaning, of history and culture, of moral responsibility and the value of human experience? Johnson...(is) the creator of the most refined and challenging philosophical literary art our country has likely ever known."
So, no, I don't think I made any "mistakes" given my particular, individual mission as an American writer/artist/philosopher/educator. I worked mindfully over four decades not to do that.