庚 Gēng — the Yang Metal Day Master

What the classics read it as

Yang Metal. Ore and blade — 庚 is the unfinished weapon, the metal that is hard before it is useful.

「庚金帶煞，剛健為最」. Geng metal carries 煞, the killing edge, and for sheer hardness nothing exceeds it. The classics do not soften this. Of the ten stems it is the one described in the vocabulary of weapons, and the two things it needs are the two things a blade needs.

What it loves: 「得水而清，得火而銳」 — with water it runs clean, with fire it takes an edge. Water here is what is expressed and given away; fire is pressure. Both are required, and neither is comfortable. 「土潤則生」 — moist earth gives it birth. Ground that still has water in it produces metal; this Day Master is fed by circumstances that are themselves being worked.

What it fears: 「土乾則脆」 — dry earth makes it brittle. Support with nothing moving through it turns hardness into a fracture that has not happened yet. And then the line every reader remembers: 「能贏甲兄，輸於乙妹」 — it defeats elder brother 甲 and loses to younger sister 乙. The axe takes the tree and is bound by the vine.

The character: direct to the point of cost, decisive early, and reliably worse at soft opposition than at hard opposition. The tradition considers this a structural fact rather than a temperament to work on.

The cost: it was ore first. Nothing here is finished by being left alone, and someone had to want it enough to do the work.