"Not true. In fact, not even false. Hasty generalization fallacy at work. All of our observations to date merely "confirm" that we haven't yet detected any ETI"

Yes, I personally believe they do exist. But we currently do not have any observation that confirms their existence. Hence, according to the statement of my friend, belief in alien civilizations is "unreliable". But, as you pointed out, this is not true.

Thank-you everyone for the replies. Clearly I am out of my depth here. I think many people suggested giving counterexamples. I was initially thinking of alien civilizations. All our current observations (Hubble, FERMI, SETI) confirm that there is nobody out there. But people still strongly believe in the possibility. Other people suggested mathematical proofs, theorems which were later confirmed, and consciousness; which are really good counterexamples.

StreetlightX:
"Your friend specified that his belief in the efficacy of observation comes from observing the efficacy of observation...that it is on the basis of verification that he believes in the efficacy of verification."

Exactly! I was like, wait, does that actually work? I agree with my "friend" that statements which can be verified through observation have high reliability. I also agree that statements that cannot be observed cannot reach that same level of reliability. But I don't think it follows that they necessarily have a low reliability or zero reliability.

I get it. Thanks.

"beliefs can only be considered reliable when they are backed, (somehow), by observation."

Is this observable or it is it a faith statement?