How do we know what we know?

Traditionally, knowledge has been defined as 'justified true belief' - i.e., knowledge is true belief held on adequate grounds.

We can discuss what it means for a belief to be justified, but the question I'm really interested in exploring is, 'What does it mean for a belief to be in fact TRUE?'

I've got a theory I'd like to bounce off the group, but would like to hear yours as well, if you've got one. If you don't, why not come up with one to share?