I came across this insightful Richard Feynman quote on C2.com.

“Right. I don’t believe in the idea that there are a few peculiar people capable of understanding math, and the rest of the world is normal. Math is a human discovery, and it’s no more complicated than humans can understand. I had a calculus book once that said, ‘What one fool can do, another can.’ What we’ve been able to work out about nature may look abstract and threatening to someone who hasn’t studied it, but it was fools who did it, and in the next generation, all the fools will understand it. There’s a tendency to pomposity in all this, to make it deep and profound.”
– Richard Feynman, Omni 1979

I happen to know the book he’s talking about. It’s Calculus Made Easy by Silvanus P. Thompson. It does a great job of explaining calculus in down-to-earth langauge. The book was written in 1910 and has been in print ever since. Thompson was a British electrical engineer and professor of physics. Like Feynman, his interests were very wide-ranging, and he was critical of people who tried to make subjects like mathematics look more difficult than they are. The introduction to his book is the most widely quoted passage:

“What one fool can do, another can.”
– Ancient Simian Proverb.

This pops up all over the internet, and often includes the attribution to the “Ancient Simians”, as if they were an extinct civilizations. Of course, it’s a joke. Simians are monkeys and apes, and monkeys copy each other. If one monkey can do it, another can.

He talks more about this in the book’s prologue.

Considering how many fools can calculate, it is surprising that it should be thought either a dicult or a tedious task for any other fool to learn how to master the same tricks.

Some calculus-tricks are quite easy. Some are enormously difficult. The fools who write the textbooks of advanced mathematics – and they are mostly clever fools – seldom take the trouble to show you how easy the easy calculations are. On the contrary, they seem to desire to impress you with their tremendous cleverness by going about it in the most difficult way.

Being myself a remarkably stupid fellow, I have had to unteach myself the difficult, and now beg to present to my fellow fools the parts that are not hard. Master these thoroughly, and the rest will follow. What one fool can do, another can.

It still goes on. A lot of mathematics books, and mathematics discussions are about displaying difficult methods, or making a great show of how rigorous and precise a solution is. The same people who chide the masses for being mathematically illiterate also work to discourage people from learning it.

Silvanus P. Thompson’s book is still in print 110 years after he wrote it. And, because it’s old, it’s also available in various places for free.