How much of what you know...
...Is actually instead what you think you know?
Why do you know what you know?
Where did you learn it?
What factual data is it based in?
Who taught it to you?
What was their reasoning for teaching it to you?
Have you ever thought about it?
How sure are you of what you know?
Is it possible you have been mislead?
How do you know?
Lots of things to consider when forming an independent opinion or stance on something.
So...
How much of what you know...
...Is actually what you think you know?