The 'Origin and Development of Psychology' is a series of five lectures from Sigmund Freud. The entirety of the lectures is small and I'd encourage anyone to read them (link to them here). His speaking is very interesting and accessible.
I wasn't sure what to expect from Freud. My studies in formal psychology is very limited but I have the impression that Freud's thinking is now regularly classified as pseudo science. From this, I thought that he was most likely a charlatan but that wasn't correct. Now I think that he was well meaning but his results are most charitably thought of as an early step on the road to understanding.
In the first lecture, Freud speaks of another Viennese physician named Joseph Breuer. Breuer found a young woman who was suffering from hysterics. Under hypnosis he was able to find the root causes of her distress. For example, she went through a summer almost completely unable to drink water. Even if she was thirsty, the thought of drinking repulsed her. He found a buried memory of her seeing an unsavory dog drinking out of a glass. Once this memory came out, she was able to drink again.
From this, and other experiences, Freud worked on a theory that psychological conditions are caused by stresses in early life. These stresses often become buried, or 'repressed', and work to poison the mind of normal healthy actions. Frankly, I'm not sure what modern science has to say about this. On the face of it, and in situations like the dog and the water, this makes sense. The question is just how much does it explain? Is every kink in the human psyche the result of some childhood episode? How would you test such a thing?
When we think of scientific efforts to test theories, we look for things like control groups. If every childhood has some trauma, then there would be no control group. And of course, every childhood does. It's part of the human condition that everyone, at some point, runs into some problem. And yet if those problems echo forward to create neurosis, then most everyone should have the most common ones.
Which isn't to say that I mean to kick Freud around. The questions of why we do what we do are fundamental. If a scientific approach can help us tackle them, the world will be a better place for it. Freud deserves some credit for those early steps, even if they aren't certainly in the right direction.