Iâm trying to understand better why a successful intraday strategy on one instrument wonât necessarily work on another. For example, say something works well on SPY; why wonât it always also work well on F? I understand oneâs an ETF based on an index, and the otherâs a single company stock. But is that all there is to it? After all, both go up and down throughout the day, and both are highly traded stocks. Even if F typically moves more in a day than SPY does (in relative percentage terms), I would have expected to be able to handle this simply by scaling strategy parameters like target/stop from SPY to F. Yet, in my experience, it doesnât seem to work. And - to my unseasoned eye at least - if you gave me charts for both taken on a random day, and hid the absolute values on the price axes (and didn't start the price axis at $0, so that I couldn't judge which instrument had the larger fluctuations in % terms), I couldnât tell you which chart was SPY and which was F. And the order books/ladders/DOMs for both instruments also look identical (again, ignoring the absolute price values). So why do some set-ups work on one, but not the other?