The times whereby things didn't work out the way you envisioned them to? The expectations and promises that all came to naught in the end? Those days when we thought the world conspired against us? Incidents like these where another is one too many. 

Over time we strengthen our defense; the walls grew thicker and higher, and we may retreat so far that sometimes we got lost from it. It is our instinct for self preservation, to save us from the hurt and disappointments. Learning from it, by not having expectations is to avoid disappointments altogether. Anything else that came along may just be a bonus. I've operated on that basis and I know part of me still behaves this way, the occasional cynic appears still. 

The darkest hour is before dawn, but everything will turn out fine after that. It is about waiting for it, the sunrise that brings forth the new day. And good things come to people eventually. 

Ultimately it is about not losing hope; the fragility of the heart can only deal with that much disappointments before shattering. But never lose hope. When you lose hope, you lose everything.