I just had a very long, frustrating afternoon. It didn't ruin my day, and I got through it by being friendly to the people who were making it difficult. As a result, I made it through with very little difficulty. I just took a very long time.
With that in mind, as an aspiring author, I always strive to treat other writers, agents, and editors well. I may not make their day better, but I refuse to be the person who could make it worse.
So go smile at someone today. Be friendly. You may find that it will keep your day from getting bad :)