Express the idea that 'only by doing something, something else can be achieved or realized.'
Long explanation:
The ~てこそ grammar point is used to emphasize the indispensable nature of the action expressed in the verb. It can be translated as 'only by', 'only when' or 'only if' in English. The construction shows that the realization of a fact or a situation is due only to the presence of a certain condition.