Like a slot machine paying off on every pull, the stock market’s most reliable bets lately have often been its riskiest.

Go long on a company that sounds like something Elon Musk mentioned in a tweet (but wasn’t)? Signal Advance Inc. just soared 12-fold. Lend money to a software-maker to buy Bitcoin? A Microstrategy Inc. convertible bond is up 50% in four weeks (its option is in the money). Back up the truck on bullish options after the Nasdaq 100 doubled in 24 months? Wednesday was the fourth-busiest day ever for call trading in the U.S. (the other three were last year).

Throw a dart, hit a winner, so it has lately seemed. Emboldened by Federal Reserve stimulus, vaccines and the psychological conditioning that arises when no bad patch lasts, everyone from retail newbies to institutional managers is rushing to cash in on the 10-month-old melt-up. Of course, it’s possible that all of this could continue for weeks, if not months, without so much as even a little reversal. Predicting exactly when such fevers will break is a near impossible task. But bubble warnings are starting to blare from every corner.