A roller folds or gathers the filler leaves so that channels run the length of the cigar. Too much leaf, or a leaf folded flat across the passage, and the air has nowhere to go. This is why draw is the most common structural fault and the hardest to fix after the fact.
Why is my cigar hard to draw?
Most often a compacted section of filler or a misplaced leaf — a plug. Sometimes it is humidity: a cigar held too wet swells and tightens. A draw tool run down the length will clear some plugs, gently rolling the cigar between the fingers will loosen others, and cutting a little deeper helps when the obstruction is near the cap. A genuinely plugged cigar frequently cannot be saved.
And too loose?
A loose cigar burns quickly and hot, and often unevenly, because air reaches the coal faster than the leaf can burn back to meet it. Over-drying produces the same effect in a cigar that was rolled correctly.
It is measured, not only judged
Factories test draw resistance mechanically and reject outside a tolerance. That a cigar reached a shop is evidence it passed, not that it was right.