G L Engel’s (1953) theory of homeostasis
The psychiatrist G L Engel is famous for his concept of the‘biopsychosocial model’(BPSM), which has been cited, to date, 14109 times:
Engel, G. L. (1977). The need for a new medical model: a challenge for biomedicine. Science, 196(4286), 129-136.
Much less cited but, arguably, a more interesting and significant contribution is Engel’s earlier paper about homeostasis, behavioral adjustment and the concept of health and disease. See details below:
Engel, G. L. (1953). Homeostasis, behavioral adjustment and the concept of health and disease. In R. R. Grinker (Ed.), Mid-century psychiatry: an overview (p. 33–59). C. C. Thomas.
All the phenomena of disease can be derived from interference with attempts at satisfaction of instinctual needs; inner perception of a disturbed equilibrium or unsatisfied need, with the concept of a danger signal; chemical, physiological, psychological and social adaptive devices coping with the stress; and structural or functional damage resulting from the stress and from attempts at adaptation which are inappropriate or unsuccessful.