"Seems to me that one unit of anything that is continuously divisible is sufficient to be a global money."

Prices are denominated in units of the currency. If there is only one digital dollar, then prices will continuously fall as smaller and smaller fractions of that dollar are needed to buy the same share of the economy's outputs. That fact encourages hoarding of the pennies, because they can buy more tomorrow than today, and hoarding pennies causes the barter economy to collapse for lack of demand. That's why economists fear deflation.

So, yes, gold failed because there was too little of it, which, in turn created pressure on government to find something better. Calling that a failure of discipline is like saying that cannibalism on a lifeboat results from too little discipline rather than too little food.