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.