Now Newton's Principia was possibly the best-confirmed scientific theory of all time. Popper reflected on the character of Einstein's achievement, and was led to a new account of the development of scientific knowledge. In Popper's account, science is the product not of induction, but of a process of conjecture and of refutation. Science, which for Popper is probably mankind's greatest cultural achievement, always remains conjectural in its character, and human beings are seen as inescapably fallible. All this also led Popper to a more general view of our condition.
Popper sees human beings, like other animals, as involved in problem solving.
We have various inbuilt expectations and mechanisms by which we interpret the world around us. But our expectations and our interpretative mechanisms are fallible. We need to learn by trial and error. Unlike animals, however, it is possible for man, using the descriptive and argumentative functions of his language, to construct a world of culture, outside of himself, in which he is able to externalize, and thus to criticize, his knowledge. By this means, as Popper has often said, men differ from the animals, because it is possible for man to let his theories die in his stead.