Interest rates can rise too high. At the close of the Carter Administration we were looking at rates as high as 17 percent. That puts capital out of reach for too many people, and makes the risks associated with taking on debt too great in most cases.
But interest rates can also be too low. Ever since the market crisis of 2008, the Federal Reserve has kept interest rates lower than they probably should have been, because the Fed thinks its job is not just to maintain the stability of the currency (which is its real job), but also to control inflation and battle unemployment. The longer we experienced muted economic growth under Barack Obama's high-tax, high-regulatory, anti-growth policies, the longer the Fed felt the need to keep interest rates low. The result of this was that interest rates didn't really reflect the true demand for credit, and the cost of the federal government's deficit spending was made to look lower than it probably should be.