Reproductive performance is of critical importance to the profitability of a cow-calf producer and numerous factors (e.g. heifer development, nutrition, cow body condition at calving, bull fertility, environment, etc.) affect reproductive efficiency, but the caveat to reproductive management is the things you do well do not compensate for the mistakes you make.
Instead, the mistakes you make cancel out all the things you do well. Thus to have optimal reproductive efficiency we need to evaluate the details and how they can impact efficiency.