Most textbooks are actually badly written. They are written by busy profs who don't put too much time into making the concepts easily accessible. This is becaus

Most textbooks are actually badly written. They are written by busy profs who don't put too much time into making the concepts easily accessible. This is because writing a book takes a lot of time, and the author does not get much monetary compensation back. The author gets some recognition, but by spending that much time on grant writing and paper writing, he would get much more recognition and funds. So the problem could be the book, don't blame yourself for everything. Search for the best book. Recently, I found that often the best book is an online tutorial, resource, blog. My 2 cents.