Big tech companies may be investing in blockchain. But sometimes they ought to focus on their core business. 

PayPal is one example. On Wednesday, shares of the payment giant sank nearly 25% after the company issued a lackluster earnings forecast for 2022 and axed earlier customer growth targets. The company launched a feature to buy, sell and hold bitcoin last year, and it confirmed last month it was looking into launching its own stablecoin, a type of digital asset backed by a traditional currency like the U.S. dollar. But some back-of-the-envelope math reveals how little those efforts are likely to help financial performance over the coming years.