丁 is the yin face of fire: a candle, a hearth, a lamp. Its difference from 丙 isn't strength but direction — the sun lights everyone, a lamp lights a small area, and what's in that area is seen more clearly than in daylight. 丁 needs fuel and can go out, which is exactly why it knows how to tend.
You'll recognise it here: one-to-one depth registers far more than a crowd does; you can hold attention on something fine for a long time, and that thing usually needs warmth rather than only technique; and the people you care about are few, while the degree of care would surprise you if you measured it.
Running well, 丁 is whoever actually attends to the detail: teaching one person, repairing one thing, making one place liveable. None of that scales, and people remember it for life. Blocked, 丁 burns itself to keep from going out — fuel down to the bottom and still saying it's fine; or, from fear of going out, refuses to light at all, capable and uninvested. The tradition says 丁 needs 薪, a continuing supply. So its practical lesson is checking the fuel first: your care is a finite resource and deserves to be managed like one.
