The standard instruction to condition mid-lengths and ends is not about avoiding greasiness alone. The two parts of a hair are genuinely different materials.
A single strand is not uniform
Hair grows at a slow and fairly steady rate, so the length of a strand is also a timeline. Shoulder-length hair has ends that emerged from the scalp years earlier.
Everything that has happened since is recorded there. Every wash, brush, heat session, colour service and hour of sun exposure has acted on the ends and not on the root.
The root section, by contrast, is only weeks old and has an intact cuticle, which is why it behaves so differently from the same strand a foot further down.
Sebum reaches only so far
The scalp produces sebum continuously, and it coats the hair nearest the follicle first, conditioning it naturally with a mix of oils.
Distribution depends on movement and brushing, and on hair texture. Straight hair carries oil down the shaft relatively well, while tightly curled hair carries it poorly.
The result is that the root end is already conditioned by the body and the far end receives almost nothing, which is exactly the gradient conditioner is designed to correct.
How conditioner attaches
Conditioners rely largely on cationic ingredients, which carry a positive charge. Damaged hair carries a negative charge, and the more damaged it is the stronger that charge becomes.
The ingredients are therefore drawn preferentially to the sections that need them, binding where the cuticle is lifted and leaving smoother areas comparatively untouched.
This is a genuinely selective mechanism, but it works within whatever area the product is applied to. It cannot move product from the scalp down to the ends.
What happens when it goes on the roots
At the scalp the same ingredients sit on hair that is already coated in sebum and on skin that does not need them.
The combined weight flattens hair at the point where volume comes from, which is why roots look limp within hours of an otherwise successful wash.
Build-up follows, since silicones and heavy conditioning agents accumulate faster than a mild shampoo removes them, and the hair progressively feels coated.
Where the rule reverses
Scalp treatments are a deliberate exception, formulated for skin rather than for the strand, and they are meant to be applied directly at the root.
Very dry or tightly coiled hair often needs conditioning closer to the scalp, because the natural oil gradient described above barely functions along a coiled shaft.
The principle is to match the product to the condition of the section, rather than to treat the whole length as one uniform material.