You don't know this

you think you do

You don't know this!

Most people think they know something, but in fact they didn't really know it.

How can we figure it out if we know something for sure?

If you can't write about something you don't really know it.

If you can't explain something to somebody else you don't know it.

If you can't fix something when it breaks you don't know it.

If you can't rewrite some code in a simple way you don't know it