Epistemology has become one of my pet interests. The big distinction is between beliefs that are "justified" (or have "warrant") and those that do not. Alvin Plantinga points out that to be justified, beliefs must first and foremost be formed on the basis of "cognitive faculties operating as they were intended to operate in an environment in which they were intended to operate." So the delusional Aussie fails that test. This is my problem with Flat Earthers and similar folk: Unless we assume you're simply pretending to amuse yourself, which is my charitable default position until proven wrong, your cognitive faculties are clearly not operating properly - so how seriously can we take your views on anything.
Beliefs can be solidly justified - rationally arrived at on the basis of plausible evidence and inferences - but completely wrong. It happens all the time to all of us. So "justified belief" is not "knowledge." The standard definition of knowledge is something like "justified true belief" - your beliefs are both justified and true - although philosophers continue to debate what actually constitutes knowledge.
The problem with religious belief (including atheistic nonbelief) is that we can never have knowledge. All major religions provide a basis for justified belief, or that we would not have lasted as long as they have and attracted as many sane and intelligent believers as they have. But their metaphysical "truths" simply can't be known, at least this side of the grave or the Second Coming. So we acquire as much knowledge as we can and form beliefs sufficiently strong to be called deep convictions - but they are still simply beliefs, not knowledge.
It's difficult to admit that one's most cherished beliefs that form the very foundation of his life may simply not be true, but that's the unavoidable reality when it comes to religious beliefs.
I had an amusing incident when my role as an assistant attorney general was to file paternity cases against deadbeat dads. As a newbie, I was delighted when a test came back with a 99.4% probability of the guy being dad. The main office called and said "Dismiss the case." WHAT - 99.4% probability and you want me to dismiss??? "That's not even close - it's gotta be 99.9%." Geez, I thought I had knowledge and I didn't even have justified belief!
Anytime you are ready to actually discuss your beliefs, you just let me know. Oh, but YOUR beliefs are the exception, right?