After staring at the market for too long, you start seeing what you want to see. With $1.1 trillion in market cap wiped out today and nearly 4,700 stocks down, I found myself thinking about something else as I watched the screen: options expiration is coming up, and both bulls and bears are holding their breath. Whoever moves first gets hit first.

After a drop like this, most people’s first instinct is to run. That’s normal. But the most exciting part of expiration week is right here: in the final few days before expiration, get the direction wrong and gamma can throw you off the ride. Put simply, gamma is how quickly an option’s Delta changes as the underlying moves. The closer you get to expiration—and the closer the underlying is to the strike price—the more dramatic those changes become. For example, an at-the-money option might have had a Delta of 0.5 the day before. After the underlying drops sharply by 2%, its Delta could quickly fall to 0.3 or even lower. Sellers and market makers then have to adjust their hedges as the market moves, which can amplify a decline on the way down and fuel a rally on the rebound.

The harder today’s selloff, the more unreasonable the rebound could be. I’m not telling you to buy the dip—I’m reminding you not to make decisions when emotions are running highest. A common pattern in past expiration weeks: the index plunges early in the week, crushing call positions and short-term sentiment, then snaps back in the two days before expiration as the concentration of open interest around certain strike prices prompts a wave of hedging. With little resistance in the market, the rebound comes fast. If you panic and sell at the lows along the way, you can easily get stopped out by the swings that follow.

The indexes are each doing their own thing, but what really determines the short-term direction isn’t which one fell the most today. It’s how positions are distributed on expiration day: which strikes have the most open interest, the ratio of call to put positions, where max pain lies, and which way market makers’ net exposure is tilted. Once these levels are triggered, short-term volatility can intensify. What do you think?