The pessimistic meta-induction is the argument that if past successful and accepted scientific theories were found to be false, we have no reason to believe the scientific realist's claim that our currently successful theories are approximately true.
The pessimistic meta-induction undermines the realist's warrant for their epistemic optimism (the view that science tends to succeed in revealing what the world is like and that there are good reasons to take theories to be true or truthlike) via historical counterexample.
Therefore, we can hold the realist view that our theoretical terms refer to something in the world and our theories are approximately true.
In fact, they are created by an entirely new set of premises (a new "paradigm"), and reach vastly different conclusions.
This gives greater weight to the proponents of anti-realism, and illustrates that no scientific theory (thus far) has proved infallible.