إِنَّمَا الْفَوْزُ لِلْمُجْتَهِدِ.
Success belongs only to the diligent.
Innamā commonly marks restriction, but analysis must identify what is restricted and what it is restricted to. Here the claim presents success as belonging to the diligent.
The formulation may encourage effort rhetorically; it need not function as an exceptionless empirical law about every event.