You need to do your best work. But the best work you are capable of producing isn't always the same in different circumstances. Sometimes you are tired and lack energy, so your work suffers. Sometimes you are physically ill and capable of squeezing out only a fraction of your usual skill. You did your best under the conditions you faced, but it wasn't your best work.
Most of the time you can exercise control over the two interrelated factors that allow you to do your best work: your energy level and your attention level.
Your energy level.
Some work simply requires more energy to do well. You have to be at your very best, your peak state, in order to do your best work at these tasks. As you energy level changes throughout the day, you are better suited for some work over others. You can plan your day to take advantage of the way your energy level changes. Do the work that takes the most energy to do well when you have the energy (i.e., prospecting), and do the work that you can do well without much energy when you're at an ebb (i.e., paperwork).
I have more energy early in the morning. I try to do the most important work I have to do early each day, while I have the physical and psychic energy to do it. I write early in the morning, and I handle all of my most difficult calls or meetings early in the day. As the day progresses, I plan tasks, activities and meetings that don't require as much energy. I like mornings, but your peak times may vary.
Your attention level.
