Merlin Mann has some interesting thoughts around priorities:
“You eventually learn that true priorities are like arms; if you think you have more than a couple, you’re either lying or crazy.”
He goes on to say that your priorities are what you are doing, not what you might theoretically like to do at any given moment.
“Example. When my daughter falls down and screams, I don’t ask her to wait while I grab a list to determine which of seven notional levels of “priority” I should assign to her need for instantaneous care and affection. Everything stops, and she gets taken care of. Conversely — and this is really the important part — everything else in the universe can wait.”
I like to think of this in terms of checking email at work. Any any given moment during the work day, you can work on a project, or check your email. It is true that checking your email can lead to changes in a current project, but, at the moment when you pulled yourself away from whatever “priority” you were working on to check your email (before you knew what the contents of the email – which might have simply been some company wide memo about Earth Day), your priority was checking your email, not working the project.
As Merlin says, the priority was observed, not assigned.