This exhortation is actually ambiguous, but both interpretations give insight into the Klingon way of thinking. The phrase could be advising one to take specific action to overcome sadness---that is, figure out exactly what the problem is and do something about it. On the other hand, for a Klingon, activity and vigor are associated with a sense of elation, while unhappiness is often connected to passivity or even laziness, character traits disdained by Klingons. Thus, the advice could be simply to do anything at all.