Teachers and teachings are one thing, thinking is another. Teachers and teachings encourage us to sit in the audience and ask thoughtful questions and nod thoughtfully at the sage replies, whereas thinking is a diamond bullet that pierces all veils and takes you straight to the heart of the matter. There is nothing to know about Advaita Vedanta or nonduality that you can’t figure out on your own, whereas if you go the teacher/teaching route, you can expect to spend the next however-many decades mired in the study of great sages which won’t advance your actual progress by much, if at all. There’s only ever one question we need to ask, one barrier that impedes our progress. No teacher or teaching can remove it for us, but moving forward is entirely a matter of identifying that barrier and smashing it to dust. Real spiritual progress is a long series of search-and-destroy missions with your particular Buddha waiting at the end of the line.