Concepts are like shadows, they don't exist.
Only in our minds are concepts classified. Just like a shadow is cast by an object that blocks sunlight, a concept is cast by our minds. Our minds are the real thing here, the concept is just what we use to make sense of the world. Without defining what something is, we'd be confused all the time.
Lot's of people live their whole lives with erroneous concepts that they model the world with. These concepts cause them to trip and fall because they behave on what they believe.
Are your concepts correct? How do you know? Are you casting the wrong shadow?