You can have a new idea, but you may not see all the ramifications of it. Other people will take your idea and reprocess it, reformulate it, improve it.
You can find forgotten ideas in old books, or several recent ideas and combine them, synthesise them.
You discuss ideas with other people and process and reprocess them.
You cannot read all books, but you can discuss them with other people, and often learn enough to avoid reading the book.
Old books become out-of-date; you rewrite them so people today can understand them; you improve them.
A mass of people and libraries constitute a computing, information processing machine which is superior to a single person trying to work it all out on its own.