To be mindful, all we need is to notice our breath.
Within 10 seconds, we can focus on our breath, notice the moment that we lose that focus, and then bring the focus back once again to the breath. We are mindful.
To be mind-full, all we need is to be breathing without noticing it. Within a lifetime, we can aimlessly let our foxus drift from sharp threat to shiny opportunity to numbing stimulus and so on.
We always have the choice and will always live in sequence with the effects.