The Route to Infinity (May 1952) 7 lectures.
Also known as The Technique 80 Lectures, this series a crucial discovery made by LRH: the ability of a person to make a decision. An inability to do that leaves a person in a state of maybe, which deteriorates one's ability and sanity. These lectures take apart the anatomy of "maybe" from the viewpoint of one's decisions, as Shakespeare put it, to be or not to be.
Technique 80 preceded Technique 88 as described in Scientology: A History of Man and are fundamental to its understanding.