Goodbug,
The 3 day rule states that when price closes under your last X_DEV buy (and you are now 100% invested) for 3 days, an exit may be warranted.
Or,
if price closes above your last X_DEV sell (and you are now 0% invested) for 3 days, a purchase may be warranted.
That's about as simple as I can state it.
If your setup was different than mine, that might mean you had a 3 day sell rule situation. I don't know what your particular setup was, so I can't say.