Blow it out of proportion

Pessimists exaggerate bad luck.  Optimists exaggerate good luck.

Authentic Happiness: Using the New Positive Psychology to Realize Your Potential for Lasting Fulfillment talks about how a pessimist "catastrophizes" bad luck.  They assume the bad incident is a sign of a broad general problem that will show itself in many other ways and that it will occur often in their lives.  It's as if they take the original event and they SSSTTTRRREEETTTCCCHHH it out.  

Something very specific happened once, but they stretch it out over time by thinking, "This kind of thing happens all the time".  They then make it part of their past and of their future.  Instead of limiting the event to a problem TODAY, they've just converted it into something with a past and a future.  They now feel regret for the past and anxiety for the future.  But it's all in their mind.  The actual event is simply here and now.

They also SSSTTTRRREEETTTCCCHHH the contents of the event.  The real event involved something very specific.  But they see it as proof of a much more general problem--something that is wrong with them that will affect much of their life.

Optimists do similar stretching of events, but they exaggerate good events instead, and this makes them happier and more successful than pessimists.  They stretch a good event over time, telling themselves that similar things happen all the time.  The pessimist who thinks bad luck happens all the time generates feelings of regret for the past and anxiety for the future.  The optimist who does the same thing with good luck creates feelings of gratitude for the past and hope for the future.

Optimists also stretch the contents of good event.  They see the event as proof of a more general good thing--a strength that they have, a talent that will bring them rewards for the rest of their lives.