Investor sentiment is upbeat but some strategists point to reasons for caution. This week, the Dow Jones Industrial Average crossed 30,000 for the first time, while the S&P closed at a record high. The 'positive' outlook we are seeing across markets might be due to a combination of factors: vaccine news, the likeliness of Janet Yellen being the next US Treasury secretary, and Donald Trump looking closer to conceding. But, is it all just short-lived euphoria? Katie Martin analyses in the Financial Times.