The concept and practice of mindfulness has been a central aspect of eastern philosophy since ancient times. Mindfulness means not only observing, but being open to everything that you are experiencing in the present moment (thoughts, feelings, sensory experience) in a defused and non-judgmental way. Mindfulness is a prerequisite for acceptance of anxious thoughts and feelings. The separation of self from experience, and the recognition of thoughts as separate from the things and events to which they refer both involve the mindful observation of your experience.
Our thoughts have a quality of continuous flow, like a river. When it comes to anxious thoughts and the feelings that accompany them, it is easy to be carried away by that river. Mindfulness helps us to see our thoughts as thoughts, observing them from the bank of the river without getting carried away by them.
If you consider the things that you are most often upset about, you will likely find that the majority of those things exist either in the past, or in an imagined future. Anxiety and worry often focus on events that may or may not occur in the next hour, weeks, or even years. At the moment you are imagining these events, they are images of possibilities. The present moment is very different from the imaginary future. When people are able to exist more fully in the present moment, they often find less cause for concern. Take this moment for example. You are reading this web page. Where are you right now? Are you terribly uncomfortable? Are you extremely warm or extremely cold? Are you in physical pain? Are you experiencing extreme hunger or thirst? If the answer to these questions is no, then the present moment is probably a pretty nice place to be.
Mindfulness means being willing to exist more fully in the present moment. When we do this, we often find that the present moment holds more peace and contentment than either the past or the future. Many people experience this grounding in the present moment when they play sports, when playing a musical instrument, cooking a gourmet meal, or grooming a beloved pet.
This focus on the present moment does not mean that we are distracted from anxious thoughts and feelings. Our present moment awareness will often include thoughts about the past or future. When we observe these thoughts mindfully, however, it is with the recognition that they are only thoughts, and that the past and future that they refer to are not real right now. This involves cognitive defusion (seeing thoughts as thoughts), but it also requires awareness of where we are and what is going on now. Therapists trained in ACT teach clients how to be more mindful of the present moment. Mindfulness is the "M" step in the LLAMP approach.