Why investors can’t agree on the financial outlook

The quokka, an Australian marsupial about the size of a domestic cat, has full cheeks and a curved mouth that convey the impression—often to delighted tourists—that the critter is smiling. It has been dubbed the happiest animal on Earth. Yet these days it has competition from another species: the American stock investor. The s&p 500 has already risen by 14% this year. An increase of another 10% would take the index back to its all-time high, set in January last year. Excitement about artificial intelligence has lit a fire under companies seen as potential beneficiaries.