There are potential consequences of getting C- that management was unwilling to bear, e.g. justification for renewal of contract.

As you all know, it's all a bell curve, so you need to:
1. Perform comparatively better than colleagues in your same pay grade. This means doing very well in your portfolio, above and beyond what your colleagues are doing.
2. Have ROs, DDs and directors who are willing to fight for your performance rating, and this is the important part, because this also means you need to have visibility to not just your RO, but your DDs and directors too. They need to know who you are, what you are doing, and value you enough to fight for your rating, else whatever your RO entered in WD would just get moderated down.