Freud wrote this book in 1920. Here are some representative quotations from the book:
"(T)he course of those (mental) events is invariably set in motion by an unpleasurable tension, and that it takes a direction such that its final outcome coincides with a lowering of that tension---that is, with an avoidance of unpleasure or a production of pleasure."
"If we take into account observations such as these, we shall find courage to assume that there really does exist in the mind a compulsion to repeat which overrides the pleasure principle."
"If we are to take it as a truth that knows no exceptions that everything living dies for INTERNAL reasons---becomes inorganic once again---then we shall be compelled to say that 'the aim of all life is death' and, looking backwards, that 'inanimate things existed before living ones.'"
"If, therefore, we are not to abandon the hypotheses of death instincts, we must suppose them to be associated from the very first with life instincts."
"It may be asked whether and how far I am myself convined of the truth of the hypotheses that have been set forth in these pages. My answer would be that I am not convinced myself and that I do not seek to persuade other people to believe in them."