To cultivate mindfulness really does involve and call out of us a certain constancy of motivation and purpose in the face of all sorts of energies in our lives, some from inside ourselves and some from outside, that dissipate our awareness by perpetually distracting us and diverting us from our intentions and purpose. The discipline I am referring to is really the willingness to bring the spaciousness and clarity of awareness back over and over again to whatever is going on—even as we feel we are being pulled in a thousand different directions.
Just taking this kind of stance toward our own experience, without trying to fix or change anything at all, is an act of generosity toward oneself, an act of intelligence, an act of kindness.
The word discipline comes from disciple, someone who is in a position to learn. So when we bring a certain discipline to the cultivation of mindfulness and are aware of how challenging it is to bring a sustained attending to any aspect of our lives, we are actually creating the conditions for learning something fundamental from life itself. Then life becomes the meditation practice and the meditation teacher, and whatever happens in any moment is simply the curriculum of that movement.