After earning my PhD in 1982, I spent the first 20 years of my professional career immersed in the tumultuous world of foreign-exchange markets. Today, current events are bringing back both happy and embarrassing memories.

I learned three things about currencies during that time. First, everyone may get their 15 minutes of fame (the Andy Warhol principle), but they shouldn’t expect it to last any longer than that. The forex market - the world’s biggest fruit and vegetable stall – tends to make idiots of those who think they’ve found the magic forecasting formula. That points to the second lesson: If I was “right” 60% of the time, I...