Human beings need other humans to help us process and regulate our emotions; this is the primary 'intersubjectivity' we all seek from others, the underlying need that bonds us together. Starting at approximately 3 months of age, well before the acquisition of language, the right hemisphere of an infant's brain is employing the body—via gestures, sounds and facial expressions—to send out social cues indicating its basic states—excitement, fear, surprise, etc—which the primary caregiver reads and reflects back. This exchange is vital for the infant's social development and sense of security.
However, the primary caregiver does more than simply 'mirroring' back an infant's emotional state; a caregiver, as part of the empathetic, sustained, resonant exchange, helps the infant regulate its early emotional states. It's an unconscious process, where the caretaker either decreases or amplifies a mood via reassuring facial gestures and body language; even from the earliest age we have brain functions set to read the smallest micro-expressions of other people.
There are two kinds of emotion regulation: vitalization and soothing. Vitalization is the stabilization of a positive emotional state, a joy that is sustainable yet not destructive. Soothing is the regulation of negative emotional states, such as fear and frustration, without which we might easily wind up overwhelmed. Proper emotion regulation allows us to move from one internal state to another without discordant mood swings.
There are three kinds of interpersonal connection necessary for regulation to occur: attunement, the state of paying attention to each other; sympathy, the intellectual understanding of another person's situation, which allows us to establish a connection in language; empathy, the ability to internally feel (via our mirror neurons) the emotions being expressed by another.
In our adult journeys we often lose touch with people who can provide us with emotion regulation—those with whom we feel safe to express our most troubling feelings, those who, rather than inclining to 'solve our problems' listen patiently, providing a safe container, as we express the difficult and exciting, and unconsciously help us achieve some stability amidst the upheavals of life.
Without these intersubjective connections that provide vitalization and soothing, we will seek regulation through other means, such as drugs that excite (cocaine, speed) or calming (alcohol, heroin). In our compulsive search for empathy we may mistake sex for intimacy, or the approval from others won from our accomplishments in the world as a form of emotional bonding. They are not, they are hollow enterprises that lead to addictive cycles.
Reestablishing secure connections is the point of relational mindfulness: when we sit with each other and pay deep attention to the underlying emotions being conveyed, feeling them internally, expressing them back, we provide the stability we spend our lives searching for, creating a therapeutic bond more powerful than any drug or worldly success story can possibly provide.