Here's a subtlety that catches new options traders: a stop order attached to an option triggers on the option's price — its last trade or bid — not on where SPY is. You might be thinking “get me out if SPY breaks 739,” but the broker is watching the contract's price, which behaves differently.

Why that causes premature stop-outs

Option prices are noisier than the underlying. The bid-ask spread can widen in a fast tape, and a single low print can tag your stop level even if SPY didn't move much. Set an option stop too tight and normal spread noise — not a real adverse move — knocks you out. The option is a leveraged, decaying proxy for SPY, so a stop that would be sensible on the stock can be far too tight on the contract.

You reason in SPY; your stop reasons in premium. Translate between them or the spread will make the decision for you.

Converting a SPY level into an option stop

The right way is to start from the underlying level where your idea is wrong, then translate it into a premium using the option's delta. If SPY reaching 739 (a $2 move against you) invalidates the trade, and your option's delta is ~0.40, that's roughly a $0.80 move in the option — so your option stop sits about $0.80 below your entry, not at some arbitrary premium. Give it a little cushion for spread noise. This is exactly what NoVo does automatically: you mark the SPY level, it attaches a protective stop on the option sized to that level, with room for the spread. Also weigh stop-limit vs stop-market so a fast move can't jump your stop.