$10 BOY deposit
$9 = $10 * (1.0 - 0.10) => value of $10 after one year with -10% change in price level (deflation).
$1 = $10 - $9 => nominal loss in value.
-9% => the bank's advertised APR.
$9.10 = $10 * (1.0 + -0.09) => EOY nominal value, what's in your account.
11% = $9.10 / $9.00 => your real return.
Simplifying somewhat, a real return Nominal - Inflation. If inflation is 4% and nominal interest is 7%, the real return is 3%. If inflation is -4%, and nominal 7%, the real return is 11%. To get a real return of 3% when inflation is -4%, nominal is -1% (because 3% = -1% + -4%).
That's the math: the bank pays you a premium over the prevailing changes in the price level — a real return — in exchange for your money. The problem is that you, as the holder of the original $10 in my example, are better off not depositing your money. If you accept the bank's deal, you're left with $9.10. If you ignore the bank, you're left with $10. And $10 beats $9.10 any day of the week, come inflation or deflation. Most people figure that out pretty soon when faced with the prospect, and banks quickly become unable to attract deposits. Etc., etc.
There is no such thing as real deflation from increases in efficiency. Change in the price level, inflation or deflation, is a monetary phenomenon. It's a function of the amount of money chasing the amount of goods and services produced. Holding the money supply constant while the economy grows (or shrinks) is no more "real" than changing the money supply while the economy is unchanged.
What I'm saying is very simple and uncontroversial: the money supply must grow with the economy, else there is deflation, and deflation is unsustainable due to the asymmetry in how interest works in the banking system. It is not a matter of trickery or psychology; it is a recognition of how people behave in the real world.
And, speaking of the real world, I'm also making an unassailable objective case: gold standards were tried and failed over the centuries, and today no government anywhere uses one. If you want to believe that's because governments everywhere prosper by deceiving the governed, I can only point out that they didn't used to.