I was speaking with a senior the other day who had just bought a used car. When he went to put his own licence plates on the screws were missing, and it really stressed him out. He couldn't figure out why he was so stressed over simple screws. Afterall, he reasoned, he could easily buy more at the local hardware store.
I listened attentively to this story and asked him "why do you think you are so stressed over such a simple thing?" At first he answered with "I don't know". But after a moment of reflection he started telling me about some of the much more perplexing events that had happened in his family lately. These major stressors he told me he had seemed to take in his stride. But he then realized his stress really was not about the 4 missing screws but about the much more difficult events.
The screws were simply "the straw that broke the camel's back" so to speak. Cumulative stress has a way of piling up until one day a simple screw can make you fume all day.