Fear in the Minds

I find this paragraph from a Financial Times editorial published today telling a big story:

It would be pointless, foolish and wrong to try and fix the dollar at its current level. Markets are the best way to determine exchange rates, and on a trade-weighted basis it is far from clear that the dollar has overshot its fair value. But what intervention might do is slow the decline, by putting fear in the minds of momentum investors who are selling short on margin.