I absolutely trust that I can refine the capacities of my own heart, and I inspire myself with stories I hear, and then tell, about people with incredible nobility of spirit. Like the story of the Zen teacher who, with her very last breath - in the tradition of Zen teachers who save their pithiest teaching for their last breath - said, "I have no complaints." I think about her when I hear my own mind complaining, annoyed that things aren't going the way I wanted them to. I know that not complaining doesn't mean not responding. I also know I could be proactive with a loving heart. But I still hear my mind being indignant or self-righteous, or telling itself sorrowful stories. All bad habits. All painful habits.
The best possible response to pain - to any pain - is compassion. Maybe the whole of spiritual practice rests on remembering - over and over again - that we are, after all, human beings.
Maybe if we acknowledged that we're human beings after all we wouldn't expect to feel perfect all the time and so it would feel more normal to let go of complaints. This is what it means, I think, to respond to pain - one's own pain as well as the pain of other beings - with compassion.