Suddenly a thought occurs to you. You have forgotten to do this or that, or you focus on how much work lies ahead. Suddenly you are no longer able to enjoy yourself. The body tenses. What has happened? You were in the now, but now your consciousness has shifted to a future event. You are taking care of the task in your mind at some time in the future, and you have lost your equanimity.
It is well and good to plan. Take time to do this. But when you are involved in an enjoyable task, keep your focus in the present. It is quite easy to lose your sense of peace. Merely shift your focus to the past or future. If you can learn to be entirely present, more peace will be the prize.