Why does one little thing set the tone for the day?

Why does it seem to set the tone for your entire day when a few things go wrong first thing in the morning?

Yesterday morning started with banging my knee hard enough to bleed on the corner of the cedar chest at the bottom of the bed and followed by dropping a full jar of mayo - uncovered - on the kitchen floor while making hubby's lunch. While cleaning up the mayo, I saw that our geriatric, newly incontinent cat peed in the dining room.

I finally made it to work where things like that continued. Weird phone calls, dropped supplies, and a very long meeting. I finally escaped from the hospital almost two hours late only to be accosted in the parking lot by my least favorite salesman. He had e-mailed the previous day asking for a meeting but I told him that I wouldn't have time and would need to reschedule for the next time that he was in town. He decided to stop in anyway just to see if I might have time and started to ask me questions while standing in the parking lot - in the rain - after I told him that I was leaving late and in a hurry.

This morning started at 0430 by sitting in cat barf on the sofa. I had to laugh.