Going beyond using 'Is it critical?' to deal with pressured days...
I think we can ask this question of anything that we do, or that comes our way....
Is this critical for me - for my happiness, my intellectual growth, my peace of mind, my emotional well-being, my weight program, my bank balance, my holiday plans, my dreams and aspirations, my dream home, my study program? (and anything else that is important for you)
It also helps to ask this question when faced with a choice - makes it easier, because an answer to this will surely be in alignment with your core.