Greatness doesn't equal perfection, let's not forget. Also, in talking about it as a concept it is important to recognise that it's quite nebulous - you pretty much can't ever say "this brewery was great since February 22nd" or "this brewery was great until that one bad batch on March 10th" - but just because it's difficult to pin down doesn't mean it doesn't exist. A great brewery can exist every bit as much as a great team, a great person, a great company or whatever other example you want to mention. Although of course if you want to argue that there's no such thing as any of those things either then we're just entering into pedantry, and I want no part in That sort of conversation.