Mark Epstein, in his video, explained that mindfulness allows us not to cling on situations that are pleasant. On the other hand, he also states that mindfulness helps us not to condemn what is unpleasant.
The situations may vary: it could be small or it could be life-changing situations.
Basically, he tells us that mindfulness is how we respond to different stimuli and situations. It is our emotional response.
Understand more about how mindfulness works. Watch the video here: How Not to be a Slave to Your Brain: Mindfulness for Mental Health