It is simply a part of the human condition that life will present us with challenges.  There is no escaping it.  When those challenges arrive, we have two choices:

become embittered by them
or
learn from them. 

Since no one likes to be around a bitter person and that approach is simply self-destructive, choose to learn from those experiences by keeping a positive attitude.  When you choose to learn from life’s challenges, you have the opportunity to become a richer, stronger and more interesting person.  It’s not easy, but with a positive attitude and perhaps by remembering the following expressions you can grow from those challenging times:

Illegitimati non carborundum est (Latin translation:  Don’t let the bastards grind you down!)

Rise to the occasion

When you get knocked down, pick yourself up, dust yourself off and start all over again