I am a 2nd year PhD student working on a project which involves control systems and power systems. For the next stage of my work, I have to learn about a control systems technique which I am not familiar with. It involves advanced mathematics and control systems concepts. So I picked the most well-known book in that area and started going through it. However, when was at the middle and I could not understand a certain concept which the book assumes that the reader is familiar with, I searched for some other references and ended up finding the 'best' references: lecture notes from top universities, video lectures, other books. However, at the end I am struggling to decide upon what to read, what not to read and the references which I am going to pick to learn the content which I need. Simply speaking I am overloaded with reference texts and struggling to make a judgement.
Having faced such a problem, in general, what would be the advice you could give to avoid getting 'lost' in trying to follow all the references ? How can I be selective and proceed with a single references and finish learning what is required.