You ARE your own best PD

I believe "you are your own best pd" is the best one because it all begins with you.  Your preparation, your mindset, your disposition, your desire...they all are extremely important to your success.  If you don't have a foundation of belief in what you're wanting to develop professionally, it will just be a huge waste of time.  You can cheat, do the minimum or get connected, but if YOU don't buy into it, it won't work.