Keeping positive - overcoming discouragement - is critical in all our careers, but especially for an entrepreneur. Most entrepreneurs are by their very nature optimists (otherwise why would they open their own business), but inevitably an account will go south, or a client won't pay, or something happens - maybe even in one's personal life - where you become discouraged.
There is no mantra, no easy way to just say "let's get back at it!". Instead, think to why you are doing this - why run your business. That perspective can help. It can also help to discuss with other entrepreneurs. You might find your situation is not uncommon. Just having peers can be very helpful.
For example, our Stillwater Entreprenuer Breakfast is this Thursday morning at 7:30. No cost, just time to meet with other business owners and commiserate over donuts and listen to a speaker.
Overcoming discouragement is not through a happy face calendar, but understanding why you are in the game in the first place.