One of the first accounts of the troublesome nature of learning outcomes is given in Plato's Meno.
Plato used a series dramatically constructed dialogues as vignettes to illustrate philosophical points he wished to make. In the Meno Plato describes a conversation between Socrates, Meno (hence the title), a slave boy and Anytus.
Meno puts the following problem to Socrates:
"Can you tell me, Socrates, can virtue be taught? Or is it not teachable but the result of practice, or is it neither of these, but men possess it by nature or in some other way?"Socrates and Meno proceed by agreeing that whereas they would recognise instances of virtue, as actions or as a quality in a person, it is difficult to know the essence of what it means to be virtuous.
So herein lies Meno's paradox how can we recognise examples of virtuous behaviour while not knowing the entirety, or the common form, of the concept. In other words, how can look for something (a form of knowledge) when we don't know what it is?
The important point is that Meno's initial question on how we learn virtue inevitably draws us toward a conceptual examination of the meaning of virtue itself.
In the end the pair fail to resolve the mater and later in the dialogue Plato (through Socrates) goes on to provide a theory of knowledge based on pre-existing memory and the use of questioning as a means of recollecting what was there in the first place.
Socrates uses a series of questions to elicit a mathematical proof from the slave boy as a means of illustrating his point.