Have you felt your mood change based on a task? Let's say you were performing a task and you felt down or sad, not because of the task but due to some external factor. The task was left incomplete and your mood improved and you returned to the task, maybe a day or two later. Just as you resumed the task, your mind also picked up the bad mood from where he left it and you are feeling sad again. I have just experienced it while uploading this picture AND the important thing is my mood improved again by acknowledging it. As soon as I realized there is nothing to feel sad about, I am feeling happy.