On the nature of concepts
This will probably be obvious to some of you, but it is something that could do with saying again.
When we attempt to understand reality, we use our minds to approximate it. There are a number of things that happen with approximation, however.
The most obvious problem is what to emphasize. Since we aren't covering everything, we must capture the most important details that lead to the 'best' approximation. But already we've run into an important point: we've invoked the idea of 'best', which is subjective. This is why there are multiple ways of explaining things, and even why two contradictory perspectives can be 'right'. One is emphasizing one thing, and another is emphasizing something else.
Another side of this issue is how best to represent the information. Let's take the realm of personality to make the issue more concrete. We will soon see that there is a wide range of variability in how people are. But if we categorize people, we can gain a better sense of what the differences are. The catch is that there are multiple differences to emphasize. One can emphasize differences due to culture, another due to introversion-extroversion, etc. Trying to take ALL of the differences into account is self-defeating, because ultimately we end up back where we started with everyone being an individual. But when you focus on a certain set of patterns, to say that it the "right" way to categorize is fallacious.
Hopefully I've covered enough of the idea that you have gotten a sense of the issue here.
Concepts are... categories.