Gamma measures how fast an option's delta changes as the underlying moves. On 1DTE options, gamma is at its highest — which means your directional exposure isn't fixed, it's shifting rapidly with every move in SPY. That's the defining characteristic, and the defining risk, of short-dated options.

Why high gamma cuts both ways

High gamma is why a 1DTE option can double or halve on a modest SPY move. When the trade goes your way, delta grows and gains accelerate — exhilarating. When it goes against you, delta shrinks (for the buyer) and the option can collapse fast. The same force that makes short-dated options thrilling on the upside makes them merciless on the downside.

The at-the-money spike

Gamma peaks at-the-money near expiration and drops off for deep in- or out-of-the-money strikes. So an ATM 1DTE contract is the most explosive — most sensitive to every tick. Strike selection is really a gamma decision: how much of this fast-moving exposure do you want? That interacts with pinning and dealer hedging around big strikes into expiration.

Gamma is the accelerator on a 1DTE option. It has no brake — which is why your risk plan has to.

Respecting it

You respect gamma with discipline the option itself won't give you: strict position sizing, mechanical exits that fire before a fast reversal compounds, and no "waiting it out." Because gamma moves faster than human reaction, this is a domain where mechanical execution earns its keep — reacting to the acceleration instantly, the way a system like NoVo is built to.