Why do we stress over the smallest things? I'm just curious to know: why do people stress over the smallest of issues? Not only is it common to almost everyone I know, but it is something that can drive people crazy. 

For example, getting really stressed when you can't get something to work (even if it's a simple as a new program on your computer), or stressed when you misplace your keys at home and immediately blame your partner. 

These rather simple things cause a great deal of stress (even for myself). While looking at my friends or family, stress over them cause me to realise how petty they are. Hasn't there got to be some cognitive reason for this?

I was having a discussion with my friend two days ago, when he told me these small stresses were a good thing, in that they make us forget about the big problems like recent job losses or events such as global warming.

Do we encapsulate ourselves in these petty matters as a means of protecting ourselves, or are we just selfish and ignorant?
This is highly individual, and related to the personality trait neurotocism.
From wiki:


  Individuals who score high on neuroticism are more likely than the
  average to experience such feelings as anxiety, anger, envy, guilt,
  and depressed mood.[2] They respond more poorly to stressors, are more
  likely to interpret ordinary situations as threatening, and minor
  frustrations as hopelessly difficult.
  http://en.wikipedia.org/wiki/Neuroticism