How long do you plan on doing this?
By "this", I mean the business you started, the private practice you opened, the ladder you're climbing, the recipe you're perfecting, the clothing line you're designing, the family you're planning, the neighborhood you're building.
Is this a lifelong dream? Your passionate pursuit that you want to take full time and run with until you're no longer able to run?
If so, then here is the secret to staying the course: every bad thing is not the last thing.
Sure, rejection, failure, and disappointment can be very bad things. But if you're in this for a very long time, these are not the last things.
But if you're just here to get rich quick, and that's not happening so fast, then throw in the towel and walk away.
But for those willing to get rich slowly, there's always another client, another customer, another idea, another opportunity, and another tomorrow.
You were meant to stay the course.