Did you ever hear anyone say -- or even say to yourself in convincing tones -- "I know what I think"?
But if you actually knew what you thought and if it were actually credible, why would you have any need to say so? Wouldn't you -- from an assured position -- be more likely to seek out what someone else thought? What need would there be to convince or entice or seek agreement from anyone else?
"I know what I think" sounds like an error to me. It may be pleasant in the sense that others will allow you to get away with it (they would like to imagine that they too 'know what they think'), but is it the truth?
I guess I just prefer the old silly ....
"How do I know what I think till I see what I say?"