In a wonderfully concise blog post called "When the sun is shining", Seth Godin wrote, "When the surf’s up, cancel everything else. Don’t waste it."
He wasn't actually talking about surfing, though.
He noted that certain days are going to feel more productive than others and that when you realize you're "in the zone" on any given day, you should cancel all of your less-essential tasks and focus on the most important work you can do.
I fully agree with this line of thinking, but I'm going to suggest a corollary to Godin's point I'd argue is just as true: if you're not "up to the task" on any given day, trying to force yourself to be productive will rarely be an effective use of your time.
We don't always have the luxury of putting off our work until we're in a flow state; some deadlines just can't be moved.
But there's a huge difference between creative or analytical tasks that need your complete focus and administrative tasks you can do regardless of how productive you're feeling.
Granted, if it's on your calendar, it probably needs to get done eventually. But given the choice between struggling with a task for three hours when you're not focused or finishing that same task in 30 minutes when you are, what option is the better use of your time?
The trick is knowing when your work can wait.
I seem to have torn a muscle in my shoulder at the gym last week and, five days after my injury, I'm still struggling to sit at my computer for more than 30 minutes.
I had several blog posts planned for this week; all of them would have been highly relevant to marketers... but all of them would have also required more time at my computer than I felt I could tolerate.
And when I got Seth's email in my inbox, I took it as a sign from God(in) that I should save those blog ideas for the future and write this (much shorter) post instead.
When you're "in the zone", make the best use of that time to do the work that matters most.
But when you're not, and what you need to do can wait, then let it wait.
Important is not the same as urgent.