Here is a good joke to emphasize this point:
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Little Johnny used to hang out at the local corner market. The
owner didn't know what Little Johnny's problem was, but the boys
would constantly tease him.
They would always comment that he was two bricks shy of a load,
or two pickles short of a barrel. To prove it, sometimes they
would offer Little Johnny his choice between a nickel (5 cents)
and a dime (10 cents) and Little Johnny would always take the
nickel -- they said, because it was bigger.
One day after Little Johnny grabbed the nickel, the store owner
took him aside and said, "Little Johnny, those boys are making
fun of you. They think you don't know the dime is worth more than
the nickel. Are you grabbing the nickel just because it's bigger"
Slowly, Little Johnny turned toward the store owner and a big
grin appeared on his face and he said, "Well, if I took the dime,
they'd stop doing it, and so far I've saved $20...!"