When Jerome Powell presided over his first policy move as chairman of the Federal Reserve on Wednesday, it was against a backdrop of very good economic news: Unemployment is low and falling; inflation is low and stable; financial markets remain buoyant.

That is also the bad news.

That’s because there are a lot more ways for the economy to get worse than to get better. Mr. Powell faces the tricky task of trying to keep growth going, and his success as the nation’s most powerful economic policymaker will depend on his ability to judge the various risks to the current expansion.

Within the announcement that the Fed will raise its interest rate target a quarter of a percentage point to a range of between 1.5 percent and 1.75 percent, there are signs that Mr. Powell and his colleagues think they can lead the nation to even greater prosperity while keeping the inevitable risks created by that growth — inflation and financial bubbles — under control.

If all goes according to plan, this would imply that the United States economy in 2019 and 2020 will be the healthiest it has been in half a century. Fed officials project the lowest unemployment rate since 1969, paired with more modest inflation than was experienced that year.