In the absence of central bank independence, monetary policy can at any time be exposed to political pressures, motivated, for example, by short-term or short-sighted policy considerations, to boost output temporarily in the short run at the expense of higher inflation in the longer run.
The public will, however, understand this problem and expect higher inflation from the outset, so that the perceived short-term trade-off between inflation and output will be negated and a permanently higher inflation rate will ensue as the only certain outcome.