There's a difference between thinking you can tell the difference or convincing others that you can tell the difference, and actually being able to tell the difference.
Nowhere is this difference more strikingly demonstrated than in the studies that have been done on wine tasting.[1]
An example from the article:
Hodgson isn't alone in questioning the science of
wine-tasting. French academic Frédéric Brochet tested the effect of
labels in 2001. He presented the same Bordeaux superior wine to 57
volunteers a week apart and in two different bottles – one for a
table wine, the other for a grand cru.
The tasters were fooled.
When tasting a supposedly superior wine, their language was more
positive – describing it as complex, balanced, long and woody. When
the same wine was presented as plonk, the critics were more likely
to use negatives such as weak, light and flat.