Every now and then, one of your characters opens up a little and says something that you didn't expect.
The Forwarder is usually suspicious and calculating - cynical to the core. Perhaps that comes from a core belief of self reliance.
The quote differentiates between the two similar sounding concepts - but points out what the character sees as a key difference. Confidence, we receive through successes. Small at first, they grow over time but that success always relies on a positive external response. Self-belief, on the other hand, must not rely on others as it is what propels you forward against challenge and rejection.
While the two are closely related, it is possible to have one without the other... Or so The Forwarder believes, at least.