Day traders getting rich buying trendy companies from solar power to cloud computing are defying two decades of money-losing history in ETFs that follow the approach. Stuffed with overvalued stocks, exchange-traded funds targeting the hottest investment themes actually lost as much as 5% per year on a risk-adjusted basis between 2000 and 2019, according to new research. It should serve as a reminder that good times don’t last, yet the speculative euphoria surrounding thematic funds keeps growing. One out of every three dollars flowing to U.S. equity ETFs in January has gone to the sector at $12.6 billion in total.