"Extraordinary claims require extraordinary evidence"

I was thinking about that famous saying of Carl Sagan's. It didn't take me long to realize that...well, what the hell is that supposed to mean?

"Extraordinary claims." What makes a claim extraordinary? I'm guessing that's supposed to refer to claims about the supernatural or God, but to call such claims 'extraordinary' is to take for granted the assumption the only the physical is real, and that therefore anything that suggests otherwise must be considered 'extraordinary'. So, why is only the physical real?

"Extraordinary evidence." This is where things get out of whack. If the evidence for an 'extraordinary' claim is also 'extraordinary', then how is one supposed to obtain any such evidence? How you know what counts as 'extraordinary evidence' if the claim itself is subject to suspicion in the first place?

Now, granted, the statement itself isn't necessarily /bad/ per se, it only presumes a number of premises that may or may not be true. Sadly, it seems a lot of people aren't even aware that there are premises to be held beforehand; the statement becomes a bald assertion masquerading as an argument.