Here is one definition of mindfulness from the Buddha himself:
And what, monks, is the faculty of mindfulness? Herein, monks, a noble disciple is mindful and is endowed with the highest prudence in mindfulness; he is one who remembers and recollects even what is done or said long ago. This, monks, is called the faculty of mindfulness.
— S V 197 (Source)
This short film illustrates another definition of mindfulness:
Mindfulness can mean many things, but central to the definition is deep and abiding awareness of what is actually going on, what is actually being thought and perceived, what is being said and what is being heard. Buddhists practice basic mindfulness in ways shown in the film, but we can also be mindful of how we communicate, how we listen and how we speak.
How can we be mindful of how we listen and speak? One way is to pay attention to ourselves. But if we only pay attention to ourselves, we will become solipsists or narcissists. We can also pay attention to others, but how do we normally do that?
Most people pay attention to others by using heuristics as Anderson Cooper does in the film linked above. He is very sophisticated, smooth, pleasant, and surely a good listener. But what that really is is an act, a professional mixture of American semiotics and American heuristics, slightly individualized in Cooper.
Cooper is not deeply aware of the people he is interviewing, though he may be moved by what they say. At best, he can only be aware of what he hears and how he interprets that. Similarly, the mindfulness master in the film, Jon Kabat-Zinn, is not a mind-reader. He cannot be any more deeply aware of others than Cooper can, or than others can of him. Yes, some people have more life experience or are smarter than others, but this only increases their deep awareness a little bit, if that. It might even lead them to worse deep awareness.
The only way to be deeply aware of another person—to be deeply mindful of what they are saying or hearing—is to ask them. And the only way to do that deeply is to do FIML.
If you just ask in the usual ways and they just answer, you will experience an exchange like the one in the film. Interesting, but there is no profound subjective data coming from either Cooper or Kabat-Zinn.
If we rely exclusively on cultural heuristics like those in the film to interact with our closest friends, we will succeed in interacting with them solely on that level*. And when we are restricted to that level, as most of us are, we cannot be deeply mindful of any other human being.
We can be mindful of what they are wearing what we think they said or meant or felt, but not them. Only FIML gives us deep access, mindful access, to others. And in the sense that how we communicate with others affects how we communicate with ourselves—how we understand ourselves—we can only become deeply aware of ourselves if we practice FIML with at least one other person. FIML might even be called “dynamic mindfulness.”
* Adding quantity—many exchanges with another person—does not fix the problem. Your relationship will look and feel more complex, but it still is not one characterized by deep awareness.