The shape of a season is decided before the first style is sketched. How many options each category carries, how much of the range is new versus carried over, and how the buy spreads across sizes — these are line-plan decisions, and they set the ceiling on how well the assortment can possibly sell. Design fills the shape; it rarely rescues a bad one.
Option count: breadth versus depth
Every category faces the same trade-off: more options spread demand thinner across styles, fewer options concentrate it. Over-optioning is the quiet killer — it inflates the buy, fragments the size buys, and leaves a long tail of styles that never earn their place and end up in markdown. The discipline is to give each category enough newness to feel fresh without diluting the buy behind any single style below the depth it needs to sell through.
A line plan makes this visible: option count by category, against the planned buy, so no category is over-optioned and under-bought.
Newness versus carryover
Newness is a balance, not a maximum. Too little and the assortment feels stale and gives the customer no reason to return; too much and the range is full of unproven options carrying markdown risk. Carryover — proven styles that sell — is not a failure of creativity; it is the stable base that funds the bets. The healthy line plan states the newness ratio explicitly per category rather than letting it drift out of the design process.
Buy to the curve, not the average
An assortment that sells in aggregate can still fail at the size level. The line plan sets option count and buy units; the size curve decides whether those units are sellable. Buying to the curve — heavier in the core sizes, lighter at the ends — is what keeps the styles in stock where demand actually is, through the full-price window. An even split is the most common way a healthy-looking buy turns into an end-of-season markdown.
The plan is one object, or it drifts
The reason assortments drift from plan is rarely a single bad call; it is that the line plan, the buy, and the size plan live in separate files that stop agreeing the moment one of them changes. Keeping them as one connected view — option count, newness, buy units, and size curve reconciled together — is what keeps the assortment that was planned the one that actually ships.