Ask any trader who blew up an account what killed them, and almost nobody says "I was wrong too often." They say "I was wrong at the worst possible size."
A losing streak is not bad luck. It is arithmetic, and it is coming for every method that has ever existed. Position sizing is the only thing that decides whether you are still at the screen when it ends.
Suppose you win 60 out of every 100 trades. That is a genuinely good hit rate. The chance that any particular run of five trades is all losers is 0.4 × 0.4 × 0.4 × 0.4 × 0.4, which is about 1 in 100.
That sounds rare until you notice how many five-trade windows there are in a year. Take two trades a day on SENSEX weeklies and you will see roughly 500 such windows in twelve months. A one-in-a-hundred event, offered five hundred times, is not an event. It is a Tuesday.
Picture a man running a vada pav stall outside a station. Every morning he decides how much batter to make. If he makes a normal batch and it rains, he loses a day's margin and opens again tomorrow.
If instead he spends his entire month's float on one enormous batch because yesterday was busy — and it rains — he does not have a bad day. He has no stall. Nothing about his cooking changed. Only the size did.
Losses do not undo symmetrically. Lose 20% and you need 25% to get level. Lose 50% and you need 100%. The hole gets steeper faster than the ladder gets longer.
| Capital lost | Gain needed just to get back to level |
|---|---|
| 10% | 11.1% |
| 25% | 33.3% |
| 50% | 100% |
| 65% | 186% |
| 80% | 400% |
Now run ten straight losers through two different sizing choices. Same trades, same method, same wrongness — only the risk per trade differs.
The green trader has a bad month. The red trader has a different life. Neither of them predicted the market any better than the other.
SENSEX weekly options trade in lots of 20, with strikes every 100 points and expiry on Thursday. So the sizing question has a concrete answer, and it works backwards from your stop-loss, not forwards from your enthusiasm.
The formula is one line:
Lots = (capital × risk %) ÷ (stop-loss in premium points × 20)
Say the account is ₹3,00,000 and you are willing to risk 2% on a trade, which is ₹6,000. Say your rule is that you are wrong if the premium falls 22 points from entry.
Notice what did not enter that calculation: how confident you feel, whether the last trade won, or whether the premium is ₹120 or ₹450. Widen the stop to 40 points and the same ₹6,000 budget buys you 7 lots, not 13. The stop and the size are one decision, taken together, before you click.
Two honest caveats, because option buyers face risks a clean formula hides.
First, a stop-loss is an instruction, not a guarantee. In a fast tape the fill can come several points worse than the trigger, so your real risk per trade is usually a little larger than the number in your spreadsheet. Size as though your stop will slip, because sometimes it will.
Second, Thursday is not a normal day. On SENSEX expiry, time decay accelerates hard and premiums can go from ₹60 to near zero in minutes. A position sized comfortably on Monday can behave very differently on expiry afternoon.
Everyone arrives at the market looking for a better entry. Almost nobody arrives looking for a smaller size. But entries only decide whether a single trade wins. Size decides whether you get to take the next hundred.