At the site of the 2010 Chilean mine disaster, the son of miner Florencio Avalos burst into tears when his father was brought safely to the surface. Later that month, Caylee Anthony’s grandmother was shown weeping over her granddaughter’s death. How can two such totally different events—one joyful, one tragic—both elicit tears?

This question puzzles many clinicians, including some who are considered experts in the field of emotional expression. The problem is that few of us have received explicit training in theories of emotion. Therefore, our notions about tears and other forms of emotional release are still partly based on “steam-kettle thinking”—the culturally pervasive but biologically absurd notion that emotions are stored quantities of energy, which, like steam, wreak havoc when bottled up too long or released too abruptly. Our everyday language is rife with steam-kettle metaphors. We talk about “blowing off steam,” being “flooded with emotion,” “boiling over” with rage, and “feeling drained” after a good cry. The Freudian theory of catharsis is basically a steam-kettle model, and so are various expressive therapies, such as psychodrama, primal scream, reevaluation counseling, and Gestalt therapy. Similarly, remnants of steam-kettle theory can be found in current approaches toward regulation, stress reduction, and anger management.

The history of the field’s views on emotional release harks back to the days when skulls were trephined to release evil…