libgen.org is one of the most important sites on the internet at the moment. Yes it's illegal. But it enables you to gain knowledge and have your textbooks if you want to learn something. If you don't have the money for textbooks and no library at hand you are in a worse position. I'm sure that a lot of people started their career and deep understanding of internet technologies by reading illegal downloaded books and eating everything that is in them.
I first try to find a book without paying. If I read a good chunk of it, if it is any good I buy the book. Otherwise I would have to pay a fortune for all the books I browse and probably may not end up reading.
I generally use the regular library first, but I've had to resort to libgen in a few cases where: 1) no library in my country has the book; and 2) the book is out of print. Without that possibility, I would have had to either not read the book, or travel somewhere with more libraries (like the U.S.).
