Zero brokerage was never zero cost.
01
The spread is a real fee, just an invisible one. It is missing from the contract note because you pay it in the fill price, not as a charge. Buy at the ask, sell at the bid, and the gap is gone before the stock has moved a rupee.
02
It scales with two things you control. How thin the stock is, and how often you churn it. A 4 pct round trip flipped a few times a year quietly outruns the extra return you switched in to chase.
03
This is the unglamorous case for liquid names, sized positions, and trading on a rule instead of an itch. Every round trip you do not take is a fee you simply keep.
The fee did not disappear when brokerage went to zero. It just moved off the contract note and into the price, where almost nobody thinks to look.