Checking Out Hypotheses

The sun is shining outside. I know that as a fact because I see it through my window. I trust my senses. Are my thoughts similarly "facts" that can be proven and known by others?

No. We may automatically assume that what we think is true and as provable as the information that we glean through our senses. However, our thoughts are not facts. They are the results of a cognitive process that filters incoming information. This filter in turn is affected by our physical state, emotions, and memory.

So view your thoughts as hypotheses that need to be checked out and verified. Just because you think it doesn't mean it's true.