I came to that same conclusion a few years ago. Sometime in college I was pretty happy, felt I was making good progression on real knowledge in a field. Now, a few years later - I'm not sure what I know is real and true, which are high order approximations, and which are flat out wrong, but still right enough to not cause too many problems.

an example: in grade school you learn how to mix colors, primary colors with paints, etc. then a little later, in middle school you learn no.. for light based, its not the same type of addition. then a little later you learn there are like an infinite possible primary colors - then a little later you learn color is actually a frequency or combination of frequencies, and you start asking yourself if your friend detects these colors the same way you do. does red to you really look blue to your friend.

it just gets weird.