being mindful takes great concentration. you can (and maybe should) be mindful in nearly all of your actions. i have to exercise my brain muscle in nearly every interaction to remain mindful. i have a ton of stuff going on in my head; that does not lead to clear thinking! the brain didn't evolve to multitask! so when dealing with stressful situations i let my emotional self drive the bus and she is a terrible driver. but if i can go back to listening to my breaths, slowing them down then refocusing to the at hand experience, i can sort it out much more quickly than if emotional ruby is terrorizing the proverbial streets.
i learned something interesting today about how the mind works. and it relates to math and philosophy! i learned that the adult brain is still incapable of negating nothing! you must have something to negate! in being and nothingness, sartre starts out by considering a temporal process of negation. a guy walks into a cafe looking for his friend, pierre. "in order to comprehend Pierre's absence, [...] requires a negative moment by which consciousness constitutes itself as a negation." (63) sartre goes on to say that one must posit in the mind that "I am conscious of Pierre not being here." nothing does not exist in the world as something tangible. nothingness is a lack of the presentation of a tangible object to consciousness.
sartre's idea is applicable to understanding interactions of humans. since the mind cannot comprehend negations as anything less than the object and a concept, when you are directing someone, err suggesting something, using negations or negative iterations are counter productive. to say "do not yell at me" is actually planting yelling, then the annihilation of yelling in the brain, which is one more step than the brain needs. it would be easier to internalize "please use your calm voice with me" as a directive to get what you'd like accomplished.
to be mindful takes energy and practice. try being mindful of negations for a week. when you catch yourself slipping into DON'Ts, instead redirect the behavior towards the end goal you're seeking.