My trick is surrounding myself with other professional project managers and producers. I have a fantastic group of kindred spirits that I can lean on from time to time. These are former coworkers, friends, all around kick-ass people. They are crucial for my sanity. They are what allows me to keep the faith when it starts to waiver.
The great thing about this support team is they are very empathetic and in most cases reach out to me before I get the energy to reach out to them. They can sense I need the atta boys.
OK, take a deep breath, in with the good air, out with the bad air. Go forth and surround yourself with a solid support group!
Here's the quote that I go to often. It sums it up.
Finish each day and be done with it. You have done what you could. Some blunders and absurdities have crept in; forget them as soon as you can. Tomorrow is a new day. You shall begin it serenely and with too high a spirit to be encumbered with your old nonsense.