Why is it easier to ruminate over hurt feelings than it is to bask in the warmth of being appreciated?

Because your brain evolved to learn quickly from bad experiences, but slowly from good ones.
 
You can change this.
 
Life isn’t easy, and having a brain wired to take in the bad and ignore the good makes us worried, irritated, and stressed, instead of confident, secure, and happy. But each day is filled with opportunities to build inner strengths and Dr. Rick Hanson, an acclaimed clinical psychologist, shows what you can do to override the brain’s default pessimism.
 
Hardwiring Happiness lays out a simple method that uses the hidden power of everyday experiences to build new neural structures full of happiness, love, confidence, and peace. You’ll learn to see through the lies your brain tells you. Dr. Hanson’s four steps build strengths into your brain—counterbalancing its ancient negativity bias—making contentment and a powerful sense of resilience the new normal. In mere minutes each day, you can transform your brain into a refuge and power center of calm and happiness. You can hardwire in happiness.