The current performance review system is broken. I have never seen bell curve working. It has a reverse effect. In large organization, HR pushes to fit all the employees in bell curve, which demotivates many employees. Success Factor is used by many companies, where employees set their goals in the beginning of the year, but goals are never static (fixed) for an organization hence employee evaluation on the basis of these goals are flawed. Most of the time YER ratings only reflect the previous month achievements. Managers often forget the best deliveries during earlier part of the year and only remember previous quarter deliverables.
I personally think, leaders (not managers) can motivate employees. Leaders always mentor, coach and inspire employees. They never consider the failure as negative if an employee learns from it.
Personally, Weekly/bi-weekly 1:1 worked best for me where we discuss what is going well, what can be done better. I listen to their concerns, provide an approach to resolve them, challenge them, provide them stretched assignments and have a balanced friendly relation with them. Leader has to develop the mutual trust with his employees to win the loyalty. No evaluation/feedback system can achieve this.
One should always keep a log for every employee 1:1 meetings. This tail can help connecting the dots and bridge the gap. If an employee is not performing well, we should consider providing candid feedback and provide some tips - how to improve on specific issues, send him for training. If he doesn't improve after all these efforts, then one should involve HR for decisions.