@mikeburns It's not really a tall claim at all. "Fewer" only makes sense if the thing in question can be counted, i.e. is a "count noun." The word "less" is used with non-count nouns, adjectives, adverbs, etc.

There are examples of idiomatic phrases that don't follow this rule ("one less problem") but they are exceptions. I'm not advocating for prescriptive grammar or anything but the two words definitely do not mean the same thing.