I don't have the answer but I do believe that our moods greatly influence our interpretations of the events during our day. The expression "wearing rose colored glasses" comes to mind for people who don't want to acknowledge the darker side of life, so why not consider the opposite? Wearing dark glasses.
Some days, for whatever reason, we put on our rose colored glasses. Little things don't bother us and we can take the bigger stuff with a grain of salt. Our perspective is good; the bigger picture is easy to see and small events are recognized for what they are: small events. Other days we don our dark glasses: little issues irritate us and it feels like the whole world is out to get us. Things don't have their usual flow and we feel out of sorts. It's easy to take things more personally, whereas if we had been wearing our other glasses it might be easier to see that some days shit just happens. It's not all about us.
In a perfect world we'd all have bifocals, or maybe one lens of each, for balance. But as it is we have to settle for being aware that some days we're wearing our rose-colored glasses and some days we have on our dark ones and that the events in our day don't change; it's our perspective that does.