Short and sweet:
Got a thing that's vague, not things discrete
Molten gold, or poop of bull, or wheat,
That you cannot...
...Count, nice and neat?

OK, yes...
Why is TT telling us this mess?
For collective lump, then we use "less"
I have less gold
(But more BS)

Can... you... count it through:
"One, three, two"?
Here's what we do:
Eu-...-ros... pounds or bucks?
Well, aw, shucks!
Then we use "few (...-ew ... -ew... -er...)

Fewer peas
We have more of those, but fewer, these [1]
He gets fewer Fives and Fours than Threes
Few parodies --
-- Of TT's please

Have... you... got it now?
Sheep or cow: then, "fewer", use
But... for... "open range"
Or for "mange": "less". Don't confuse!

Quality:
"Chicken" TT has less nerve than she
("Turtle: fewer nerves than chimpanzee")
'Cause courage can't ...
...Be counted, see? [2]

Use "less" to indicate degree...



[1] Or "fewer of these"

[2] We wouldn't say, "She has three courages". So courage or nerve (as a quality) is compared by using "less", as opposed to "nerves", which are individual, countable things in your body.

To sum up: If it's one vague lump, quantity, or quality, like courage, gold, wheat, oil, or money, use "less":
"Russia exports less wheat than the U.S., but the U.S. should use less oil, and its government should spend less money."
If it's individual units that could be counted, use "fewer":
"There are fewer grains of wheat in a pound than in a kilogram." "Fewer barrels of oil burned..." "Fewer tax dollars spent..."
The difference in the second example is that grains, barrels, and dollars are individual units that can be counted. (Yes, you can count "money", but only if you count it in units, as euros, pounds, or dollars, etc.)

Making any sense here?

*Extra Credit*: The gurus tell us that it's OK to use "less" if the number of countable things is referring to a single measurable quantity: "Less than two weeks before exams" ("Less time than...") or "Less than 200 million barrels of oil in the reserve" ("Less oil than...") .