Let me start by saying something as obvious in theory as it is neglected in practice: If we’re going to be helpful, we need to know what help is being asked for, or needed. It’s amazing how often we breeze through this step, usually because we assume we know. For instance, sometimes we will talk about something difficult with a friend or partner or therapist because we want to share it and be heard. We don’t want advice or solution, yet that’s what we often get—even from clinicians who should know better! Being truly helpful depends on discerning what’s needed, and acting accordingly.
In the clinical language of a physician or psychotherapist, this is the diagnostic step. Before treating someone, we try to be as clear as we can be about what’s going on. Sometimes it’s simple, but often it’s not; in therapy it can take time to discover what’s truly ailing someone, since they themselves may not know. There are lots of attempts to make things simple, by trying to reduce everything to ‘genes cause disease’ or ‘stress causes disease.’ Or by imagining that different people suffering similar symptoms can be treated in the same way. Sorry, reductionists, but pathology (like health) is almost always more complicated.
For the most part, suffering and disease—and their contrary, health—result from the interaction between an individual’s particular vulnerability (genetic, epigenetic, psychic, etc) on the one hand, and environmental stressors on the other. This general approach to pathology is called “the diathesis-stress” model; diathesis from Greek means “arrangement” or “disposition.” Think of it as your “constitution.” Stress in this context refers to an external force that affects our constitution, for better or worse. Thus, whenever we’re trying to help, we need to understand what someone brings to the situation and what situational pressures they're facing.

Hippocrates (c. 460-370 BCE), the ‘father of modern medicine,’ understood this in a way that modern medicine and psychiatry—historically driven by reductionist impulses—are only now fully acknowledging. You can see the modern diathesis-stress model writ large in his thinking. The opening paragraph of his medical treatise, “Concerning Airs, Water, and Places,” conveys an expansive vision of how the environment (natural and social and behavioral) bears on our mental and physical health. There’s something beautiful and inspiring about the example he sets here, about how much careful attention is needed if we’re to understand and help.
Whoever wishes to investigate medicine properly, should proceed thus: in the first place to consider the seasons of the year, and what effects each of them produces (for they are not at all alike, but differ much from themselves in regard to their changes). Then the winds, the hot and the cold, especially such as are common to all countries, and then such as are peculiar to each locality. We must also consider the qualities of the waters, for as they differ from one another in taste and weight, so also do they differ much in their qualities. In the same manner, when one comes into a city to which he is a stranger, he ought to consider its situation, how it lies as to the winds and the rising of the sun; for its influence is not the same whether it lies to the north or the south, to the rising or to the setting sun. These things one ought to consider most attentively, and concerning the waters which the inhabitants use, whether they be marshy and soft, or hard, and running from elevated and rocky situations, and then if saltish and unfit for cooking; and the ground, whether it be naked and deficient in water, or wooded and well watered, and whether it lies in a hollow, confined situation, or is elevated and cold; and the mode in which the inhabitants live, and what are their pursuits, whether they are fond of drinking and eating to excess, and given to indolence, or are fond of exercise and labor, and not given to excess in eating and drinking.