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Jasper
The points you make regarding the attraction of the market toward a big strike price are valid can come in very hy when the markets are trading near those points.
Here's a more accurate depiction of what's going on though.
When banks buy or sell options most of the time they are going to hedge or completely offset those positions. They are not taking naked one-sided bets. That's not their game. The hedging can take a number of paths.
One very common path is the delta hedge in which the bank uses the option delta (in essense the % likelihood of the option being triggered) to establish a hedge position. As the market moves the delta will change which means the bank will be adjusting their position according. If the bank has sold an option based on the market reaching a higher level their delta hedge would involve being long in the spot market. As prices rise - increasing delta - they will be d to buy more in the spot market to keep their hedge in line. This is a part of the attraction toward the strike. The bank's own activity to a certain degree is self-fullfilling. This is in fact the exact opposite of defending a strike.
I used to work in the fx options spot markets. There was always a lot of chatter about big expiries important strike prices. Most of the time it amounted to very little. The fact of the matter is you can't know how big any strike really is given that the market is primarily inter-bank commercials can play a big role as part of their hedging operations.
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Author - The Essentials of Trading
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